How do you calculate the area of a circle?

Square the radius and multiply by pi: area = π × r². A circle with radius 5 has area π × 25 ≈ 78.54 square units.

What is the area of a triangle?

Multiply the base by the height and divide by two: area = (base × height) / 2. A triangle with base 6 and height 4 has area 12.

How do you find the area of a rectangle?

Multiply the length by the width: area = length × width. A rectangle 8 by 5 has area 40 square units.

Area Calculator — Circle, Square, Rectangle, Triangle & More

The distance from the centre to the edge.

Radius

78.54 u² AREA

π × 5² ≈ 78.54

How the math works

Circle

area = π × r² · circumference = 2 × π × r

Square & rectangle

square = side² · rectangle = length × width

Triangle & parallelogram

triangle = (base × height) ÷ 2 · parallelogram = base × height

Trapezoid & ellipse

trapezoid = ((a + b) ÷ 2) × height · ellipse = π × a × b

Frequently asked

What unit is the answer in? Area comes out in square units — if you measure in metres, the area is square metres (m²). Just use the same unit for every measurement.

Why is my triangle answer half what I expected? The triangle formula divides by two because a triangle is half of a rectangle with the same base and height.