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Geometry · Perimeter

Perimeter Calculator

Find the perimeter of a square, rectangle, triangle, or circle.

Perimeter Calculator

Choose a shape, enter its measurements, then select Calculate.

How these calculations work

A square's perimeter is 4 times its side. A rectangle's perimeter is 2 times the sum of its length and width. A triangle's perimeter is the sum of its three sides — the three lengths must satisfy the triangle inequality (each side shorter than the sum of the other two) to form a real triangle. A circle's perimeter (circumference) is 2π times its radius.

Examples

A square with a 5-unit side has a perimeter of 20. A 30×20 rectangle has a perimeter of 100. A 3-4-5 triangle has a perimeter of 12. A circle with a 5-unit radius has a circumference of about 31.42.

About these formulas

These are standard geometry formulas — no external source citation is needed for them.

Related tools

More calculators are on the way — browse everything planned on the Home page.

Frequently asked questions

What units does the result use?

Whatever unit you enter your measurements in — the result is in that same unit.

Why does the calculator say my input is invalid?

A required field is empty or not a number, a measurement is zero or negative, or — for a triangle — the three side lengths you entered can't actually form a triangle (one side is too long compared with the other two).