How to Calculate the Area of a Rectangle, Circle or Triangle
Each shape has its own area formula, but all three are simple. This guide explains them with examples you can check.
What is the Area Calculator?
Pick a shape and enter only the measurements that shape needs. A rectangle uses length times width, a circle uses pi times the radius squared, and a triangle uses half times base times height. The tool checks that you gave the dimensions for the shape you picked before calculating.
How to use it
- Choose a shape.
- Enter the dimensions that shape needs.
- Calculate to see its area.
Worked example
A rectangle 5 by 4 has an area of 20.
What is the area of a rectangle 5 long and 4 wide?
Multiply length by width: 5 times 4 is 20. So the rectangle covers 20 square units. A circle of radius 5, by comparison, covers about 78.54 square units, and a triangle with base 10 and height 4 covers 20 square units.
Frequently asked questions
Do I need to fill in every box?
No. Only the dimensions for your chosen shape are used, so leave the others blank.
What units is the answer in?
Square units matching whatever unit you measured in: centimetres give square centimetres, metres give square metres, and so on.