Area Calculator
Calculate the area of a rectangle, circle, triangle, trapezoid, ellipse, parallelogram, or regular polygon in any unit — including acres and hectares.
Cómo usar esta calculadora
- 1Choose the shape you are measuring.
- 2Pick the unit you measured in and use it consistently for every dimension.
- 3For a triangle or parallelogram, the height must be measured perpendicular to the base — not along a slanted side.
- 4Read the area, and use the table for square metres, acres, or hectares.
Cómo funciona
Area formulas
Rectangle A = l × w Circle A = π r² Triangle A = ½ b h Trapezoid A = ½ (a + b) h Ellipse A = π a b Parallelogram A = b h Regular n-gon A = n s² ÷ (4 tan(π/n))
Most of these reduce to base × height. A parallelogram has exactly the area of the rectangle you get by sliding the slanted end across, so the slanted side length is irrelevant — only the perpendicular height matters. A triangle is half a parallelogram. A trapezoid is a parallelogram whose base is the average of its two parallel sides.
Ejemplo resuelto
A 24 ft × 18 ft room has an area of 432 square feet, which is 40.13 square metres or about 0.0099 acres. Its perimeter is 2 × (24 + 18) = 84 feet.
Area Calculator: la guía completa
Perpendicular height is not the slanted side
For triangles and parallelograms, the height in the formula is the perpendicular distance from the base to the opposite vertex or side. It is not the length of a slanted edge, and for an obtuse triangle it can even fall outside the shape.
Measuring a slanted side and calling it the height is the most common source of inflated area results. If you only know the three side lengths of a triangle, Heron's formula gives the area without needing a height: with s as half the perimeter, A = √(s(s−a)(s−b)(s−c)).
Land area: acres, hectares, and square feet
An acre is 43,560 square feet — historically the area a yoke of oxen could plough in a day, which is why it is such an awkward number. A hectare is a clean 10,000 square metres, or about 2.471 acres.
For property work, remember that a square acre is roughly 209 feet on a side, and a standard American football field including both end zones is about 1.32 acres. Those anchors make it easy to sanity-check a survey figure before trusting it.
Irregular shapes and the subtraction method
Real rooms and real lots are rarely one clean shape. The reliable approach is decomposition: draw the outline, split it into rectangles and right triangles along the natural corners, compute each piece, and sum them.
For a shape with a bite taken out — an L-shaped room, a lot with a pond — it is often faster to calculate the full bounding rectangle and subtract the missing piece. Both routes give the same answer, so use whichever needs fewer measurements.
Preguntas frecuentes
How do I calculate the area of an irregular room?
Divide it into rectangles and triangles along the corners, calculate each area separately, and add them together. Subtract any part that is not usable, such as a built-in island or a stairwell opening.
How many square feet are in an acre?
Exactly 43,560 square feet. One acre is also about 4,047 square metres, or 0.4047 hectares. The conversion table above gives all of these automatically for whatever shape you calculated.
What is the difference between area and perimeter?
Area measures the surface enclosed by a shape, in square units — it tells you how much flooring, paint, or turf you need. Perimeter measures the distance around the outside, in linear units — it tells you how much fencing, trim, or edging you need.
Why is the ellipse perimeter approximate?
Unlike a circle, an ellipse has no exact closed-form perimeter — it requires an elliptic integral. This calculator uses Ramanujan's second approximation, which is accurate to better than one part in a billion for any realistic shape.