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200 free calculators for finance, math, construction, health, education, and dates — accurate, mobile-friendly, and explained step by step.
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Mortgage, interest, investment, and money calculators for real financial decisions.
37 calculators
- Mortgage CalculatorEstimate your monthly mortgage payment, total interest, and yearly amortization from home price, down payment, interest rate, and loan term.
- Compound Interest CalculatorSee how your savings grow with compound interest. Calculate the future value of an initial deposit plus monthly contributions at any interest rate.
- ROI CalculatorCalculate return on investment (ROI) from your initial investment and final value, including net gain and annualized return.
- CD CalculatorCalculate the maturity value and interest earned on a certificate of deposit (CD) from your deposit, interest rate, term, and compounding frequency.
- APR CalculatorFind the true annual percentage rate (APR) of a loan once fees are included, plus the monthly payment and total cost. Compare loans on a fair basis.
- 401(k) CalculatorProject your 401(k) balance at retirement from your salary, contribution rate, employer match, and expected return — with a year-by-year growth schedule.
- Roth IRA CalculatorProject the tax-free value of a Roth IRA at retirement and see exactly how much the tax shelter is worth compared with an ordinary taxable account.
- Credit Card Payoff CalculatorFind out how long it takes to clear a credit card balance, how much interest it costs, and what monthly payment would clear it by a chosen date.
- Future Value CalculatorFind what a lump sum and regular deposits will be worth in the future at a given rate of return, and see the split between money paid in and interest earned.
- Sales Tax CalculatorAdd sales tax to a price or work backwards from a tax-inclusive total to find the pre-tax amount and the exact tax paid.
- Tip CalculatorWork out the tip, the total, and each person's share of a restaurant bill — with the option to tip on the pre-tax amount and round the split.
- Salary CalculatorConvert a wage between hourly, daily, weekly, monthly, and annual pay, with unpaid holidays and vacation taken into account.
- Income Tax CalculatorEstimate US federal income tax, Social Security and Medicare, your effective and marginal rates, and take-home pay from your gross salary.
- Loan CalculatorCalculate the monthly payment, total interest, and full amortization for any loan — and see how much an extra monthly payment saves.
- Simple Interest CalculatorCalculate simple interest and the final balance on a principal at a fixed rate over time, and see how it compares with compound interest.
- Savings Goal CalculatorFind the monthly deposit needed to reach a savings target by a set date, given what you've already saved and an expected rate of return.
- Break-Even Point CalculatorFind how many units you must sell to cover your costs, from fixed costs, price per unit, and variable cost per unit — plus the profit at any volume.
- Inflation CalculatorSee how inflation erodes the buying power of money over time: what a sum will be worth in the future, what a basket will cost, and the total loss.
- Retirement CalculatorProject your retirement savings from current balance and monthly contributions, then estimate the yearly income it could safely provide at retirement.
- Net Worth CalculatorAdd up your assets and subtract your debts to find your net worth, with a breakdown of what you own, what you owe, and your debt-to-asset ratio.
- Rent vs Buy CalculatorCompare the total cost of buying a home against renting over the years you'll stay, accounting for the mortgage, upkeep, appreciation, and equity on sale.
- Debt-to-Income Ratio CalculatorCalculate your debt-to-income ratio — the front-end (housing) and back-end (total debt) figures lenders use — and see where you fall against typical approval limits.
- Mortgage Refinance CalculatorCompare your current mortgage with a refinance to find the monthly saving, how many months to break even on closing costs, and the lifetime interest difference.
- Annuity CalculatorTurn a lump sum into a stream of equal payments, or find the lump sum a desired payment needs, using the present value of an annuity at a chosen rate and term.
- Dividend CalculatorCalculate the income and yield from a dividend-paying holding, and project how the income and yield-on-cost grow over time as the dividend increases.
- Auto Loan CalculatorCalculate a car loan's monthly payment and total interest from the price, down payment, trade-in, sales tax, rate, and term — the true cost, not just the payment.
- Amortization CalculatorSee how a loan amortizes: the monthly payment, total interest, and a year-by-year schedule of how each payment splits between interest and principal.
- Emergency Fund CalculatorFind how big your emergency fund should be from your monthly expenses, how much more you need, and how many months of saving it takes to get there.
- Rule of 72 CalculatorEstimate how long money takes to double at a given return using the Rule of 72, or the rate needed to double in a set time, with the exact figure for comparison.
- Overtime Pay CalculatorCalculate gross pay with overtime: regular pay plus time-and-a-half (or any multiplier) on the extra hours, with the effective hourly rate for the week.
- Wage CalculatorConvert pay between hourly, weekly, monthly, and annual, in either direction, using your hours per week and weeks per year — to compare a wage against a salary.
- Margin & Markup CalculatorFrom cost and selling price, find profit, gross margin, and markup — the two percentages, measured against price and against cost, that businesses constantly mix up.
- Present Value CalculatorFind the present value of a future sum — what it's worth today after discounting at a chosen rate — with the total discount and the discount factor.
- Down Payment CalculatorCalculate the down payment on a home from the price and percentage, the loan amount that remains, whether you avoid mortgage insurance, and how long to save.
- CAGR CalculatorCalculate the compound annual growth rate (CAGR) between a starting and ending value over a number of years, with the total return and growth multiple.
- Investment Return CalculatorCalculate the profit and percentage return on a stock or fund trade from the shares, buy and sell prices, trading fees, and dividends received.
- Loan Payoff CalculatorSee how adding extra to your monthly loan payment cuts the payoff time and the total interest, compared against paying the minimum.
- Percentage CalculatorSolve any percentage problem: find X% of a number, what percent one number is of another, or the percent change between two values.
- Percent Off CalculatorCalculate the sale price after a discount. Enter the original price and percent off to see the final price and how much you save.
- Average CalculatorCalculate the average (mean), median, sum, minimum, and maximum of a list of numbers. Paste or type values separated by commas or spaces.
- Standard Deviation CalculatorCalculate sample or population standard deviation, variance, and mean from a list of numbers.
- Ratio CalculatorSimplify a ratio to its lowest terms or solve a proportion for the missing value. Enter A:B to reduce it, or A:B = C:D with one blank to solve.
- Percent Error CalculatorCalculate percent error between an experimental and a true value, or percent difference between two measurements, with the working shown step by step.
- GCF & LCM CalculatorFind the greatest common factor and least common multiple of any list of numbers, with prime factorizations and the full list of common factors.
- Quadratic Formula CalculatorSolve any quadratic equation ax² + bx + c = 0 with real or complex roots, and get the discriminant, vertex, axis of symmetry, and factored form.
- Fraction CalculatorAdd, subtract, multiply, or divide two fractions and get an exact simplified answer, plus the mixed number, decimal, and percentage forms.
- Slope CalculatorFind the slope between two points along with the line's equation, intercepts, angle, length, midpoint, and perpendicular slope.
- Probability CalculatorCalculate the probability of two events happening together, either one happening, neither happening, and the chance of at least one success across repeated trials.
- Combinations & Permutations CalculatorCalculate nCr and nPr with and without repetition, plus factorials — and see exactly when order matters and when it does not.
- Statistics CalculatorGet the mean, median, mode, range, variance, standard deviation, and quartiles of a data set in one step, with the working shown.
- Z-Score CalculatorCalculate a z-score from a value, mean, and standard deviation, and convert it to a percentile and tail probabilities on the normal distribution.
- Logarithm CalculatorCalculate the logarithm of a number in any base, plus the natural log (ln) and common log (log₁₀), and go the other way with exponents.
- Percentage Change CalculatorFind the percentage increase or decrease between two numbers, with the exact change, the direction, and the multiplier — and see why a rise then an equal fall doesn't return you home.
- Exponent CalculatorRaise any base to any power — including negative, zero, and fractional exponents — and see the result with the rule that explains what the exponent means.
- Scientific Notation ConverterConvert any number to and from scientific notation, plus engineering notation and E-notation, with the order of magnitude and expanded standard form.
- Prime Number CalculatorCheck whether a number is prime, and get its prime factorization, number of divisors, and the nearest prime numbers above and below it.
- Square Root CalculatorFind the square root or any nth root of a number, with the simplified exact radical form, a perfect-power check, and the negative root for even roots.
- Proportion CalculatorSolve a proportion a/b = c/x for the missing value by cross multiplication, and check whether two ratios are equal — the maths of scaling and conversion.
- Sequence CalculatorFind the nth term and the sum of an arithmetic or geometric sequence from the first term, the common difference or ratio, and the number of terms.
- Modulo CalculatorCompute the remainder (modulo) and quotient of a division, with both the truncated and floored conventions shown so the negative-number cases are unambiguous.
- Rounding CalculatorRound a number to decimal places, significant figures, or the nearest multiple, with round-up and round-down shown alongside the standard rounded result.
- Factorial CalculatorCompute the factorial n! — the product of all integers up to n — with the number of digits and trailing zeros, for any n from 0 to 170.
- Confidence Interval CalculatorCalculate a confidence interval for a mean from the sample mean, standard deviation, and size, with the margin of error and standard error at your chosen confidence level.
- Sample Size CalculatorCalculate the survey sample size needed for a chosen margin of error and confidence level, with a finite-population correction for smaller populations.
- Linear Equation CalculatorFind the equation of a line through two points in slope-intercept form (y = mx + b), with the slope, x- and y-intercepts, and the line's angle.
- System of Equations CalculatorSolve a system of two linear equations in two variables (a₁x + b₁y = c₁, a₂x + b₂y = c₂) using Cramer's rule, with a diagnosis of no or infinite solutions.
Area, volume, and surface area for every common shape, with the formula shown.
11 calculators
- Volume CalculatorCalculate the volume of a cylinder, box, sphere, cone, pyramid, or capsule in any unit, with the formula and every common unit conversion shown.
- Area CalculatorCalculate the area of a rectangle, circle, triangle, trapezoid, ellipse, parallelogram, or regular polygon in any unit — including acres and hectares.
- Surface Area CalculatorCalculate the surface area of a box, cylinder, sphere, cone, or capsule, split into lateral and end areas, with every common unit conversion.
- Triangle CalculatorSolve a triangle from three sides or two sides and the included angle — get every angle, the area, perimeter, heights, and the triangle's classification.
- Pythagorean Theorem CalculatorSolve a right triangle with a² + b² = c²: find the hypotenuse from two legs, or a missing leg from the hypotenuse, with the angles, area, and perimeter.
- Distance Between Two Points CalculatorCalculate the straight-line distance between two points from their coordinates, with the midpoint, slope, and the horizontal and vertical distances.
- Circle CalculatorEnter a circle's radius, diameter, circumference, or area and get all the others, plus π and the exact relationships between them.
- Circle Sector CalculatorCalculate the area, arc length, chord, and perimeter of a circular sector from its radius and central angle, in degrees.
- Regular Polygon CalculatorCalculate the area, perimeter, interior and exterior angles, apothem, and circumradius of a regular polygon from its number of sides and side length.
- Cone CalculatorCalculate the volume, slant height, lateral surface area, and total surface area of a right circular cone from its base radius and height.
- Trapezoid CalculatorCalculate the area, midsegment, and perimeter of a trapezoid from its two parallel sides, height, and the two legs.
- Unit ConverterConvert length, weight, area, volume, speed, time, data, energy, and pressure between every common metric and imperial unit, with exact factors.
- Temperature ConverterConvert between Celsius, Fahrenheit, Kelvin, and Rankine instantly, with the conversion worked step by step and a reference table of key temperatures.
- Roman Numeral ConverterConvert numbers to Roman numerals and Roman numerals back to numbers, with the subtractive rules explained and each symbol broken down.
- Number Base ConverterConvert numbers between binary, octal, decimal, hexadecimal, and any base from 2 to 36, with the repeated-division working shown step by step.
- Download Time CalculatorEstimate how long a download or upload takes from the file size and your connection speed, accounting for the bits-versus-bytes gap.
- Pressure ConverterConvert pressure between psi, bar, kilopascals, atmospheres, mmHg, and inHg — the units used in tyres, weather, diving, and engineering.
- Energy ConverterConvert energy between joules, kilojoules, calories, food Calories, watt-hours, kilowatt-hours, BTU, foot-pounds, and electronvolts.
- Speed ConverterConvert speed between mph, km/h, m/s, ft/s, knots, and Mach — the units of driving, running, sailing, aviation, and physics.
- Ohm's Law CalculatorSolve for voltage, current, resistance, or power from any two known values, with the exact formula used and the full Ohm's law wheel explained.
- Electricity Cost CalculatorWork out what an appliance costs to run per hour, day, month, and year from its wattage, usage hours, and your electricity rate per kWh.
- Dew Point CalculatorCalculate dew point, absolute humidity, and how the air will actually feel from temperature and relative humidity, in Celsius or Fahrenheit.
- Molecular Weight CalculatorCalculate molar mass from any chemical formula, with per-element percent composition and a grams-to-moles conversion.
- Molarity CalculatorCalculate the molarity of a solution from mass, molar mass, and volume — or find the mass of solute needed to make a solution of a target concentration.
- Half-Life CalculatorCalculate how much of a substance remains after any time using exponential decay, from its half-life — plus the decay constant, mean lifetime, and number of half-lives.
- Specific Heat CalculatorFind the heat energy needed to change a substance's temperature with Q = mcΔT, using a built-in table of specific heat capacities or your own value.
- pH CalculatorConvert between hydrogen-ion concentration and pH, with pOH and hydroxide concentration, and see where a solution falls on the acidic–neutral–basic scale.
- Dilution CalculatorWork out how much stock solution and diluent to mix for a target concentration and volume using C₁V₁ = C₂V₂, with the dilution factor and fold dilution.
- Wind Chill CalculatorCalculate the wind chill or 'feels like' temperature from air temperature and wind speed using the official NWS formula, with the frostbite risk it implies.
- Percent Yield CalculatorCalculate the percent yield of a reaction from the actual and theoretical amounts of product — the standard measure of reaction efficiency — in grams or moles.
- Boyle's Law CalculatorApply Boyle's law, P₁V₁ = P₂V₂, to find the new pressure or volume of a fixed amount of gas at constant temperature when the other changes.
- Moles CalculatorConvert between grams, moles, and number of particles using molar mass and Avogadro's number — the core mass-to-moles conversion of chemistry.
Motion, energy, force, gravity, and waves — mechanics worked from first principles.
15 calculators
- Projectile Motion CalculatorCalculate the range, maximum height, time of flight, and impact speed of a projectile from its launch speed, angle, and height.
- Gravitational Force CalculatorCalculate the gravitational attraction between two masses with Newton's law of universal gravitation, from their masses and the distance between them.
- Kinetic Energy CalculatorCalculate kinetic energy, momentum, mass, or velocity for a moving object — and see why doubling speed quadruples the energy.
- Density CalculatorCalculate density, mass, or volume from the other two, and compare the result against water and common materials to see what would float.
- Wavelength & Frequency CalculatorConvert between wavelength, frequency, and photon energy for light and any wave, using the wave equation and Planck's relation.
- Ideal Gas Law CalculatorSolve the ideal gas law PV = nRT for pressure, volume, moles, or temperature, with pressure and volume in the units you actually use.
- Pendulum CalculatorCalculate the period and frequency of a simple pendulum from its length and gravity — or find the length needed for a given period.
- Force Calculator (F = ma)Solve Newton's second law F = ma for force, mass, or acceleration, with the result in newtons, pounds-force, and as a multiple of gravity.
- Resistor Color Code CalculatorDecode a four-band resistor's colour bands into its resistance and tolerance, with the value range it guarantees — no more squinting at the rainbow.
- Torque CalculatorCalculate torque — the turning effect of a force — from the force, lever-arm length, and angle, using τ = r·F·sin θ, in newton-metres and pound-feet.
- Hooke's Law CalculatorSolve Hooke's law F = k·x for the spring force, spring constant, or displacement, and find the elastic potential energy stored in the spring.
- Momentum CalculatorCalculate linear momentum (p = m·v) from mass and velocity, with the kinetic energy — the conserved quantity behind collisions, recoil, and propulsion.
- Voltage Divider CalculatorCalculate the output voltage of a two-resistor voltage divider from the input voltage and resistor values, with the current drawn and power dissipated.
- Free Fall CalculatorCalculate the fall time, distance, and impact velocity of an object dropped from rest under gravity, from either the height or the fall time (ignoring air resistance).
- Capacitor CalculatorCalculate the charge and stored energy of a capacitor from its capacitance and voltage (Q = CV, E = ½CV²), and the time constant with a resistor.
Your weight and age across the planets, escape velocity, orbits, light-years, rockets, and black holes.
13 calculators
- Weight on Other Planets CalculatorFind out how much you would weigh on the Moon, Mars, Jupiter, and every other body in the solar system — your weight scaled by each world's gravity.
- Age on Other Planets CalculatorSee how old you are on Mercury, Mars, Jupiter, and every planet — one planetary year is one orbit of the Sun, and each world takes a different time.
- Escape Velocity CalculatorCalculate the escape velocity of any planet, moon, or star from its mass and radius — the speed needed to leave its gravity behind forever.
- Orbital Period CalculatorCalculate the orbital period and speed of a satellite or planet with Kepler's third law, from the orbit's size and the mass it goes around.
- Light Travel Time & Distance CalculatorConvert any distance into how long light takes to cross it, and light-years into kilometres — the natural way to measure the scale of space.
- Rocket Equation CalculatorWork out a rocket's delta-v from its specific impulse and mass ratio using the Tsiolkovsky equation — and see why spacecraft are mostly fuel.
- Black Hole CalculatorEnter a mass and find a black hole's event horizon (Schwarzschild radius), its Hawking temperature, and how long it would take to evaporate.
- Star Luminosity CalculatorCalculate a star's total luminosity from its radius and surface temperature using the Stefan–Boltzmann law, in watts and multiples of the Sun.
- Telescope Magnification CalculatorCalculate telescope magnification from the focal lengths, plus exit pupil, true field of view, and the minimum and maximum useful magnification for your aperture.
- Moon Phase CalculatorFind the Moon's phase on any date — its age in days, the illuminated fraction, and the dates of the next new and full moons — from the mean lunar cycle.
- Parallax Distance CalculatorConvert a star's parallax angle into its distance in parsecs, light-years, and astronomical units — the geometric method that anchors the cosmic distance ladder.
- Angular Size CalculatorCalculate the angular size (apparent size) of an object from its actual diameter and distance, in degrees, arcminutes, and arcseconds.
- Redshift CalculatorCalculate cosmological redshift z from observed and rest wavelengths, the recession velocity (classical and relativistic), and a Hubble-law distance estimate.
- Concrete CalculatorCalculate how much concrete you need in cubic yards, cubic feet, and cubic meters — plus how many 60 lb or 80 lb bags for your slab.
- Gravel CalculatorEstimate how much gravel, crushed stone, or sand you need in cubic yards and tons for a driveway, path, or base layer.
- Square Footage CalculatorCalculate the square footage of a rectangle, circle, or triangle area — with results in square feet, square yards, and square meters.
- Mulch CalculatorCalculate how much mulch you need in cubic yards and 2 cubic foot bags to cover a garden bed at your chosen depth.
- Roofing CalculatorEstimate roof area, roofing squares, and the number of shingle bundles needed from the building footprint and roof pitch.
- Tile CalculatorWork out how many tiles and boxes you need for a floor or wall, including grout lines, a waste allowance for your layout, and the total cost.
- Paint CalculatorWork out how much paint a room needs from its dimensions, number of coats, doors, and windows — with the ceiling, primer, and total cost included.
- Stair CalculatorCalculate riser height, tread depth, stringer length, and total run from your floor-to-floor rise — with code compliance checked as you go.
- Roof Pitch CalculatorConvert roof pitch between rise-per-12, degrees, and percentage grade, and get the rafter length, slope factor, and true roof area.
- Brick CalculatorEstimate how many bricks a wall needs from its dimensions, the brick size, and the mortar joint, with a wastage allowance and bricks-per-square-metre figure.
- Fence CalculatorEstimate the posts, rails, and pickets a fence needs from its length, post spacing, and picket width, with concrete bags for setting the posts.
- Flooring CalculatorWork out how many boxes of flooring a room needs and the total cost from its dimensions, the coverage per box, and a waste allowance for cuts.
- Drywall CalculatorEstimate the drywall sheets, screws, joint tape, and compound a room needs from its wall and ceiling area, with a waste allowance for cuts.
- Wallpaper CalculatorCalculate how many rolls of wallpaper a room needs from its perimeter and height, the roll dimensions, and the pattern repeat that adds waste to every strip.
- BTU CalculatorEstimate the BTUs of heating and cooling a room needs from its area, ceiling height, sun exposure, and occupancy — sizing an air conditioner or heater correctly.
- Deck Board CalculatorEstimate how many deck boards a deck needs from its dimensions, board width, and gap, plus the total linear footage, joist count, and a waste allowance.
- Rebar CalculatorEstimate the reinforcing bar for a concrete slab: bars each way at a chosen grid spacing, total linear footage, grid intersections, and standard bars to buy.
- Wall Framing CalculatorEstimate the studs and plate lumber a wall needs from its length, stud spacing, corners, and openings — the framing material list for a partition or exterior wall.
- Excavation CalculatorCalculate excavation volume in cubic yards from length, width, and depth, plus the loose (swelled) volume to haul away and an approximate weight in tons.
- Board Feet CalculatorCalculate board feet of lumber from thickness, width, length, and quantity — the volume unit hardwood is priced by — with the total cost.
- Baseboard CalculatorCalculate the linear feet of baseboard or trim a room needs from its dimensions, minus doorways, with a waste allowance and the number of standard lengths to buy.
- BMI CalculatorCalculate your Body Mass Index (BMI) from height and weight in metric or imperial units, see your WHO category and healthy weight range.
- Macro CalculatorCalculate your daily calories and macronutrient targets (protein, carbs, and fat) from your body metrics, activity level, and goal.
- Protein CalculatorEstimate your daily protein needs in grams from your body weight and activity goal, shown as a recommended range.
- Body Fat CalculatorEstimate body fat percentage with the US Navy tape method, plus lean mass, fat mass, and where you sit against the standard fitness categories.
- BMR & TDEE CalculatorCalculate your basal metabolic rate and total daily calorie burn from height, weight, age, and activity level — with cutting and bulking targets.
- Pace CalculatorConvert between running pace, speed, distance, and finish time — with per-kilometre splits and predicted times for every standard race distance.
- Calories Burned CalculatorCalculate calories burned walking, running, cycling, or from 20 other activities using MET values — with the net figure above resting burn.
- BAC CalculatorEstimate blood alcohol concentration with the Widmark formula from drinks, body weight, and time — and understand why the number should never decide whether you drive.
- Period CalculatorPredict your next periods, ovulation date, and fertile window from your last period and average cycle length, with a six-cycle calendar.
- Child Height PredictorPredict a child's adult height from the parents' heights using the mid-parental method, with the expected range and how genetics really works.
- Ideal Weight CalculatorEstimate a healthy body weight from height and sex using the Devine, Robinson, Miller, and Hamwi formulas, alongside the healthy-BMI range.
- Water Intake CalculatorEstimate how much water to drink each day based on your body weight, activity level, and climate — with the amount in cups, litres, and ounces.
- Due Date CalculatorEstimate a pregnancy due date from the last menstrual period or conception date, with the current week, trimester, and key milestones.
- One Rep Max CalculatorEstimate your one-rep max (1RM) from a set of several reps using the Epley, Brzycki, and Lombardi formulas, with a training-percentage table for every rep range.
- Target Heart Rate CalculatorFind your training heart-rate zones from your age, using either a percentage of maximum heart rate or the more personal Karvonen heart-rate-reserve method.
- Body Surface Area CalculatorEstimate body surface area (BSA) from height and weight using the Mosteller, Du Bois, and Haycock formulas — the measure clinicians use to scale drug doses.
- Waist-to-Hip Ratio CalculatorCalculate your waist-to-hip ratio and see the WHO health-risk category for your sex — a measure of where you carry fat that BMI cannot capture.
- Calorie Deficit CalculatorEstimate how long it takes to reach a goal weight at a given daily calorie deficit, with the weekly rate of loss and the total energy that has to come from fat.
- Lean Body Mass CalculatorEstimate lean body mass and body-fat percentage from height and weight using the Boer and James formulas, or directly from a measured body-fat percentage.
- Ovulation CalculatorEstimate your ovulation day and fertile window from the first day of your last period and your cycle length, with the next period and test dates.
- Smoking Cost CalculatorCalculate what smoking costs per day, year, and over decades, plus what that money could grow to if invested instead — the financial case for quitting.
- VO2 Max CalculatorEstimate your VO2 max — the top measure of aerobic fitness — from a 12-minute Cooper run test or from your resting and maximum heart rate, with a fitness rating.
- Steps to Miles CalculatorConvert steps into distance in miles and kilometres and estimate calories burned, using a stride length worked out from your height.
- Waist-to-Height Ratio CalculatorCalculate your waist-to-height ratio and see the health-risk category — a simple central-obesity screen behind the rule 'keep your waist under half your height'.
- Pregnancy Weight Gain CalculatorFind the recommended pregnancy weight-gain range from your pre-pregnancy BMI, plus the expected gain by your current week, based on the Institute of Medicine guidelines.
- Race Time PredictorPredict your finishing time at a new race distance from a known time at another, using Riegel's endurance formula, with the equivalent pace.
- Blood Pressure CalculatorClassify a blood pressure reading into the standard categories (normal, elevated, stage 1 or 2 hypertension, crisis), with pulse pressure and mean arterial pressure.
- Cholesterol Ratio CalculatorCalculate your total-to-HDL and LDL-to-HDL cholesterol ratios and non-HDL cholesterol from a lipid panel — better heart-risk indicators than total cholesterol alone.
- GPA CalculatorCalculate your GPA on the standard 4.0 scale from letter grades and credit hours for up to 8 courses.
- Final Grade CalculatorFind out what grade you need on your final exam to reach your target course grade, based on your current grade and the final's weight.
- Weighted Grade CalculatorCalculate your overall weighted grade from individual assignment, quiz, and exam scores and their weights.
- Test Grade CalculatorConvert a test score to a percentage, letter grade, and grade points, with an optional curve and a table showing the grade for every number of mistakes.
Practical everyday tools — fuel cost, cooking conversions, sleep, unit prices, and more.
15 calculators
- Fuel Cost CalculatorEstimate the fuel cost of a trip from the distance, your vehicle's fuel economy, and the price of fuel — with round-trip and per-person totals.
- Fuel Economy CalculatorConvert fuel economy between US mpg, UK mpg, litres per 100 km, and km per litre — or work it out from the distance driven and fuel used.
- Cooking Measurement ConverterConvert between cups, tablespoons, teaspoons, millilitres, and more, and read oven temperatures across Celsius, Fahrenheit, and gas mark.
- Sleep CalculatorFind the best times to go to sleep or wake up based on 90-minute sleep cycles, so you wake at the end of a cycle feeling refreshed.
- Unit Price CalculatorCompare two products by price per unit to find the better deal, accounting for pack size and quantity — the bigger package is not always cheaper.
- Speed, Distance & Time CalculatorSolve for speed, distance, or travel time from the other two, mixing miles, kilometres, mph, km/h, and m/s with hours and minutes.
- Aspect Ratio CalculatorResize an image or screen while keeping its aspect ratio, or find the ratio of any width and height — for photos, video, and displays.
- Reading Time CalculatorEstimate how long a text takes to read silently, read aloud, or skim from its word count, plus a handy page-count and reading-speed reference.
- Coffee Ratio CalculatorCalculate how much coffee and water to use for a consistent brew from a ratio like 1:16, working from the water, the coffee, or the number of cups.
- Recipe ScalerScale a recipe up or down between serving sizes: get the multiplier and the converted quantity for any ingredient, plus what to watch when scaling.
- Bill Split CalculatorSplit a restaurant bill with tip evenly among a group, with the per-person share, tip amount, and grand total — and an option to round each share up.
- Dog Age CalculatorConvert your dog's age into human years using a size-adjusted model, with the first two years counting for much more — not the outdated 'times seven' rule.
- PPI / Pixel Density CalculatorCalculate a screen's pixel density (PPI) from its resolution and diagonal size, with the dot pitch, physical dimensions, and total megapixels.
- EV Charging Time CalculatorEstimate how long an electric car takes to charge from one battery percentage to another, based on battery size, charger power, and charging efficiency, plus the cost.
- Height ConverterConvert height between feet-and-inches and centimetres in either direction, with metres and total inches — handling the composite feet-plus-inches format.
- Age CalculatorCalculate your exact age in years, months, and days from your date of birth — plus total days, weeks, and time until your next birthday.
- Date CalculatorFind the number of days between two dates, or add and subtract days, weeks, months, and years from a date to get a new date.
- Elapsed Time CalculatorCalculate the duration between a start and end time in hours and minutes — including shifts that run past midnight.
- Days From Today CalculatorFind the date a given number of days, weeks, months, or years from today — forward or backward, counting all days or only business days.
- Work Hours CalculatorAdd up a weekly timesheet from clock-in and clock-out times, subtract unpaid breaks, and split the result into regular and overtime pay.
Built to be trusted
Fast, accurate calculators, clearly explained
01
Accurate & tested
Every formula is implemented as pure, deterministic code with automated tests — no rounding until the final display.
02
Explained, not just computed
Each calculator shows the formula, a worked example, and answers to common questions so you understand the result.
03
Fast on any device
Results update instantly as you type, with mobile-first forms and no popups in the way.
FAQ
Questions
Are these calculators free to use?
Yes — every calculator is completely free, with no account or sign-up required.
How accurate are the results?
Each calculator uses a tested, deterministic formula and keeps full precision until the final display. The formula and a worked example are shown on every page, so you can check the method yourself.
Do you store the numbers I enter?
No. Calculations run entirely in your browser — the values you type never leave your device.
Which languages are available?
The platform is fully available in English, Spanish, French, Portuguese, and Arabic, including a right-to-left layout for Arabic.
Do the calculators work on mobile?
Yes. Every page is mobile-first, and results update instantly as you type on any device.