Energy Converter
Convert energy between joules, kilojoules, calories, food Calories, watt-hours, kilowatt-hours, BTU, foot-pounds, and electronvolts.
Cómo usar esta calculadora
- 1Enter the amount of energy.
- 2Choose the unit it's currently in.
- 3Read the equivalent in joules, calories, kilowatt-hours, BTU, and more.
- 4Note the difference between the small calorie and the food Calorie (kilocalorie).
Cómo funciona
Energy conversion
1 kJ = 1,000 J, 1 kcal = 4,184 J 1 Wh = 3,600 J, 1 kWh = 3,600,000 J 1 BTU = 1,055 J, 1 ft·lb = 1.356 J convert via joules: value × factorₐ ÷ factor_b
Energy is a single physical quantity, but it is measured in a wide variety of units because different disciplines adopted their own. The joule is the SI unit, the energy of a one-newton force acting over one metre, and everything converts through it. Chemistry and nutrition use the calorie, defined by the heat needed to warm water, with the confusing wrinkle that the food 'Calorie' is actually a kilocalorie, a thousand physics calories. Electricity is billed in kilowatt-hours, the energy of a kilowatt of power sustained for an hour, equal to 3.6 million joules. Heating and air conditioning use the British thermal unit, mechanics uses the foot-pound, and atomic and particle physics use the electronvolt, an almost inconceivably tiny amount of energy suited to single particles. Converting between any of them is a matter of multiplying by the source unit's value in joules and dividing by the target's, which routes every conversion cleanly through the common base of the joule.
Ejemplo resuelto
One kilowatt-hour of electricity is 3,600,000 joules, which is 3,600 kilojoules, about 860 food Calories, or 3,412 BTU. So running a 1,000-watt heater for an hour delivers the same energy your body would use in roughly a third of a day of food.
Energy Converter: la guía completa
One quantity, many units
Energy is among the most universal concepts in science — the capacity to do work, present in motion, heat, light, chemical bonds, and mass itself — yet it is measured in a bewildering assortment of units. The reason is historical: fields developed their measurements independently before energy was understood to be a single unified quantity. Heat was measured in calories and BTU, mechanical work in foot-pounds, electricity in watt-hours, and the physics of particles in electronvolts, long before it was clear that all of these were the same thing expressed in different currencies.
The great insight of nineteenth-century physics was that energy is conserved and can be converted between all these forms, which meant the units had to be interconvertible too. The joule was adopted as the SI standard, and every other energy unit can be expressed as a fixed number of joules. This is what makes conversion straightforward: no matter how exotic the units, they all reduce to joules, so converting between any two is just a matter of going through that common base. The variety of units reflects the variety of contexts in which energy appears, not any real difference in the underlying quantity.
The calorie confusion
No energy unit causes more confusion than the calorie, because there are two of them differing by a factor of a thousand. The scientific calorie, written with a lowercase c, is the energy needed to raise one gram of water by one degree Celsius — a small amount, about 4.2 joules. The 'Calorie' on food labels, often written with a capital C, is actually a kilocalorie, equal to a thousand of those small calories. So a food item listed as 200 Calories really contains 200,000 scientific calories, or about 837,000 joules.
This ambiguity is a genuine trap. A chemistry problem and a nutrition label can both say 'calories' and mean quantities that differ by a thousandfold. The convention of capitalising the food Calorie is inconsistently followed, so context is the real guide: energy in food and diet is always in kilocalories, while energy in a chemistry or physics calculation is usually in the small calorie or, better, in joules. When converting, it is essential to know which calorie is meant. The calculator labels the food Calorie explicitly as a kilocalorie to keep the distinction clear, because getting it wrong turns a snack into the energy content of a small explosion.
Making energy tangible
Converting between energy units is not just bookkeeping; it builds intuition for how much energy different things involve, which is otherwise hard to grasp. Putting everyday quantities on a common scale reveals surprising relationships. A single food Calorie, the kind counted in a diet, is about 4,184 joules — enough to lift a small car a short distance. A kilowatt-hour of electricity, costing a few cents, packs 3.6 million joules, equivalent to the energy in roughly 860 dietary Calories, which is why electricity is such a concentrated and useful form of energy.
These comparisons illuminate real decisions and facts. Understanding that a kilowatt-hour equals a certain number of BTU lets you compare the running cost of an electric heater against a gas one. Knowing the joule content of food Calories connects diet to physical work — climbing stairs, for instance, burns a calculable number of Calories. At the other extreme, the electronvolt, the tiny unit of particle physics, shows just how little energy individual atoms and photons carry, and how staggeringly many of them are involved in any macroscopic amount of energy. By translating energy into whatever unit is most meaningful for a given context, conversion turns an abstract physical quantity into something you can reason about concretely.
Preguntas frecuentes
How many joules are in a kilowatt-hour?
3,600,000 joules. A kilowatt-hour is the energy of 1,000 watts sustained for one hour, and since a watt is a joule per second, that's 1,000 × 3,600 = 3.6 million joules. It's the unit on your electricity bill.
Is a food Calorie the same as a calorie?
No — the food Calorie (capital C) on nutrition labels is a kilocalorie, equal to 1,000 scientific calories (lowercase c). So a 200-Calorie snack is 200,000 small calories, or about 837,000 joules. Diet and food use kilocalories; chemistry and physics use the small calorie or joules.
How do I convert between energy units?
Route through the joule, the SI unit. Multiply your value by the source unit's value in joules, then divide by the target unit's. For example, 1 kWh is 3.6 million joules, which divided by 4,184 J per food Calorie is about 860 Calories.
What is a BTU?
A British thermal unit is the energy to raise one pound of water by one degree Fahrenheit — about 1,055 joules. It's used mainly in heating and air conditioning to rate the capacity of furnaces, boilers, and AC units. One kilowatt-hour is about 3,412 BTU.