Area is the amount of flat surface a shape covers. You need it to buy flooring, paint, turf or fabric, to compare land plots or to work out pressure and material weight. Each shape has its own formula, so choosing the right one is the first step.
How to use the Area Calculator
- Shape
- Side length a
- Length a
- Width b
- Base b
- Height h
- Radius r
- Semi-axis a
- Semi-axis b
- Base a
- Base b
- Height h
- Diagonal p (e₁)
- Diagonal q (e₂)
- Angle α
- Outer radius R
- Inner radius r
- Number of sides n
Results update as you type, and everything is calculated in your browser.
How it works
Choose the shape and only the measurements that shape needs will appear. Every length can be entered in its own unit; the area is converted to the unit you choose. Angles can be entered in degrees or radians.
Inputs explained
| Field | What to enter |
|---|---|
| Shape | Choose one: Square, Rectangle, Triangle (base and height), Circle … |
| Side length a | Units: cm, m, mm, in, ft, yd … |
| Length a | Units: cm, m, mm, in, ft, yd … |
| Width b | Units: cm, m, mm, in, ft, yd … |
| Base b | Units: cm, m, mm, in, ft, yd … |
| Height h | Units: cm, m, mm, in, ft, yd … |
| Radius r | Units: cm, m, mm, in, ft, yd … |
| Semi-axis a | Units: cm, m, mm, in, ft, yd … |
| Semi-axis b | Units: cm, m, mm, in, ft, yd … |
| Base a | Units: cm, m, mm, in, ft, yd … |
| Base b | Units: cm, m, mm, in, ft, yd … |
| Height h | Units: cm, m, mm, in, ft, yd … |
| Diagonal p (e₁) | Units: cm, m, mm, in, ft, yd … |
| Diagonal q (e₂) | Units: cm, m, mm, in, ft, yd … |
| Angle α | Units: °, rad, π rad, grad, turn |
| Outer radius R | Units: cm, m, mm, in, ft, yd … |
| Inner radius r | Units: cm, m, mm, in, ft, yd … |
| Number of sides n | A number |
Example values
How the main result changes when Side length a changes and everything else stays at the example values above:
| Side length a (cm) | Area (cm²) |
|---|---|
| 2.5 | 40 |
| 3.75 | 40 |
| 5 | 40 |
| 6.25 | 40 |
| 7.5 | 40 |
| 10 | 40 |
Formula
Square a² · Rectangle a·b · Triangle b·h/2 · Circle πr² · Sector r²α/2 · Ellipse πab
Trapezoid (a + b)h/2 · Rhombus/kite pq/2 · Regular n-gon na²/(4 tan(π/n))
Worked example
Inputs — Shape: Rectangle; Length a: 8 cm; Width b: 5 cm.
Results — Area = 40 cm².
Key terms
- Area
- The size of a two-dimensional surface.
- Apothem
- The distance from the centre of a regular polygon to the middle of a side.
Frequently asked questions
How do I find the area of an irregular room?
Split it into rectangles and triangles, find each area and add them.
Why is the area in square units?
Area multiplies two lengths, so cm × cm = cm².
What is the area of a circle with radius 5 cm?
π·5² ≈ 78.54 cm².
How do I convert m² to ft²?
Multiply by 10.7639 – or simply change the unit menu.