Area Calculator
Calculate the area of common shapes using the selected dimensions.
Choose a shape
Select a rectangle, triangle, or circle and enter the dimensions. Keep all measurements in the same unit. The result is expressed in square units, so a unit conversion may be needed before comparing different shapes.
Common formulas
Rectangle area equals length multiplied by width. Triangle area equals one half multiplied by base and height. Circle area equals pi multiplied by radius squared. Use the radius rather than the diameter in the circle formula, or divide the diameter by two first.
Worked example
A rectangle that is 8 units long and 5 units wide has an area of 40 square units. A triangle with base 8 and height 5 has an area of 20 square units.
Frequently asked questions
Frequently Asked Questions About Online Calculators
Can I calculate a circle from its diameter?
Convert diameter to radius by dividing by two before applying the circle formula.
Why are the units squared?
Area measures two dimensions, so the unit is multiplied by itself.
Does the calculator include irregular shapes?
No. Use a suitable decomposition or specialist method for irregular boundaries.