Perimeter Calculator
Perimeter of a rectangle, square, or triangle — or the circumference of a circle
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Quick summary
Pick a shape and enter its dimensions to get the perimeter (the distance around it) with the formula shown. A rectangle is 2 × (length + width); a square is 4 × side; a triangle is the sum of its three sides; and a circle's perimeter — its circumference — is 2 × π × radius. Units are whatever you enter (feet, meters, inches); the result is in the same unit.
Reviewed by Simple Calculators TeamLast reviewed
How to use this calculator
- Enter the inputs requested by the calculator.
- Choose the units or options that match your situation and review the assumptions.
- Run or update the calculation to see the result.
- Review the result, breakdown, and formulas shown on the page.
- Check the inputs, units, dates, and limitations before saving or sharing the result.
Frequently asked questions
How do I find the perimeter of a shape?
Add up the length of every side. For a rectangle that simplifies to 2 × (length + width); for a square, 4 × side; for a triangle, side A + side B + side C. For a circle, the equivalent measure is the circumference, 2 × π × radius. This calculator applies the right formula for the shape you pick.
What is the difference between perimeter and area?
Perimeter is the distance around the boundary of a shape (a length, in feet or meters); area is the space inside it (in square units). You'd use perimeter for fencing or trim and area for flooring or paint. They're different measurements with different units.
What is circumference?
Circumference is the perimeter of a circle — the distance around it — calculated as 2 × π × radius (or π × diameter). π is approximately 3.14159. This calculator computes it when you choose the circle shape and enter the radius.
What units does the perimeter calculator use?
Whatever unit you enter. If you type dimensions in feet, the perimeter is in feet; in meters, it's in meters. Just keep every dimension in the same unit — don't mix feet and inches in one calculation.
Key terms
- Perimeter
- The total distance around the edge of a two-dimensional shape.
- Circumference
- The perimeter of a circle: 2 × π × radius.
- Triangle Inequality
- Any two sides of a triangle must together exceed the third, or it can't close.
Methodology, sources & limitations
This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.
For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.