How to Calculate Area of Common Shapes
Short answer
Rectangle = L×W; triangle = ½×base×height; circle = πr². Keep units consistent. Example: triangle base 10, height 6 → area 30.
Area questions dominate school maths and DIY planning. Check answers with the area calculator.
Core formulas
- Square: side²
- Rectangle: length × width
- Triangle: ½ × base × height
- Circle: π × radius²
- Trapezoid: ½ × (b1+b2) × height
- Ellipse: π × a × b
Units
Convert inches and centimetres first with the unit converter.
Fractions in dimensions
Plans often use fractional inches — the fraction calculator helps before you multiply.
Related: how to convert inches to cm.
Related: how to convert miles to kilometers.
Related: how to calculate percentage of a number.
More practice
Change the inputs, rewrite the formula from memory, then confirm with the tool. Keep units consistent and read the disclaimer on tax or health pages before acting on a number.
Frequently asked questions
What is the area of a circle?
πr².
How do I find triangle area without the height?
You need a perpendicular height or another method (Heron’s formula) with all three sides.
Is area the same as perimeter?
No. Perimeter is distance around; area is surface inside.
Can I calculate acreage?
Convert the area to square feet or metres, then to acres (1 acre = 43,560 ft²).