This area calculator finds the area of five common plane shapes. Select a shape and use the dimension fields indicated by its formula; unused dimensions are ignored, keeping one compact tool suitable for different geometry problems.
How to use this calculator
For a square, enter side A. A rectangle uses A and B. A triangle uses base A and height. A circle uses radius A. A trapezoid uses parallel bases A and B plus height. Results are in square units matching the input.
Formula & calculation method
Square A²; rectangle AB; triangle AH/2; circle πA²; trapezoid (A+B)H/2The calculator applies the selected shape's formula directly. It requires positive primary dimensions and nonnegative secondary fields where applicable. Because no unit conversion is performed, all dimensions must use the same linear unit.
Worked example
A rectangle with sides 10 and 5 has area 50 square units. A circle with radius 10 has area approximately 314.159 square units using π, not a rounded approximation such as 3.14.
Why this is useful
Shape-specific formulas and units make the result easy to verify. The calculator reduces manual errors in homework, material estimation, and quick planning while showing which dimensions belong to each shape.
Limitations to keep in mind
Correct results depend on using perpendicular height where required and a radius rather than diameter for circles. Real-world irregular shapes may need to be divided into simpler regions before using these formulas.
Frequently asked questions
What unit does the result use?
It uses square units of whatever linear unit you entered. Centimeter inputs produce square centimeters, and meter inputs produce square meters.
Does circle area use radius or diameter?
Use the radius in field A. If you have the diameter, divide it by two first.
Which height should a triangle use?
Use the perpendicular distance from the selected base to the opposite vertex, not necessarily the length of a slanted side.