Area Calculator for Square, Rectangle, Circle & Triangle

Area Calculator

This tool calculates the area of six shapes: square, rectangle, triangle, circle, trapezoid, and parallelogram. Pick a shape, enter its dimensions, and the calculator returns a plain numeric area you can use in whatever unit you measured in, whether that is centimeters, meters, or feet.

How each shape is calculated

Each shape needs a different set of measurements. A square needs only one side length, since all four sides match. A rectangle needs its width and height. A triangle needs its base and the height measured at a right angle to that base, not the length of a slanted side. A circle needs its radius, the distance from the center to the edge. A trapezoid needs the two parallel sides plus the height between them. A parallelogram needs a base and a height, the same inputs as a rectangle, except its sides can lean instead of meeting at right angles.

Worked examples

A rectangular patio measuring 4.2 by 5.5 meters covers 4.2 × 5.5 = 23.1 square meters. A circular flower bed with a 1.8 meter radius covers π × 1.8², which comes out to 10.1788 square meters once rounded to four decimal places. A triangular garden bed with a 6 meter base and a 3.5 meter height covers ½ × 6 × 3.5 = 10.5 square meters.

Formulas and example values

Each formula below can be copied straight into a notebook or spreadsheet.

Square: Area = a²
Rectangle: Area = w × h
Triangle: Area = ½ × b × h
Circle: Area = π × r²
Trapezoid: Area = ½ × (a + b) × h
Parallelogram: Area = b × h