Perimeter Calculator

What is perimeter?

Perimeter is the total distance around the outside of a shape. For a circle it is called the circumference. Perimeter uses ordinary length units such as feet or meters, unlike area, which uses square units.

Perimeter formulas

Shape	Formula
Rectangle	P = 2 × (length + width)
Square	P = 4 × side
Triangle	P = a + b + c
Trapezoid	P = a + b + c + d
Regular polygon	P = number of sides × side length
Circle	C = 2πr = πd
Ellipse	Ramanujan's approximation

Worked example

A garden 8 m long and 5 m wide has a perimeter of 2 × (8 + 5) = 26 m, which is how much edging or fencing it needs.

Uses for perimeter

• Fencing a yard or garden
• Baseboard, trim or crown molding for a room
• Edging for flower beds and paths
• Framing a picture or a quilt border

Frequently asked questions

How do you find the perimeter of a rectangle?

Add the length and the width, then multiply by 2. A 10 by 4 rectangle has a perimeter of 2 × 14 = 28.

How do you find the circumference of a circle?

Multiply the radius by 2π, or multiply the diameter by π (about 3.1416).

Is perimeter the same as area?

No. Perimeter is the distance around a shape. Area is the space inside it.

Why is the ellipse perimeter an approximation?

There is no simple exact formula for an ellipse. Ramanujan's formula is accurate to many decimal places for everyday shapes.

What units does perimeter use?

The same units as the side lengths you enter: inches, feet, meters and so on.