Perimeter Calculator
Find the perimeter of a rectangle, square, triangle or circle from its dimensions — the total distance around the shape.
How it works
Rectangle 2(l + w) · Square 4s · Triangle a + b + c · Circle (circumference) 2πr
Perimeter is the total distance around the outside of a two-dimensional shape — the length of fence, trim or edging it would take. For straight-sided shapes you simply add the sides: a rectangle has two lengths and two widths, a square has four equal sides, and a triangle sums its three. A circle’s equivalent is its circumference, 2πr, the distance once around the curve.
Worked example
A rectangle 5 long and 3 wide has perimeter 2 × (5 + 3) = 16 units. Switch to a square of side 5 and it becomes 4 × 5 = 20; a 3-4-5 triangle gives 3 + 4 + 5 = 12; and a circle of radius 4 has circumference 2 × π × 4 = 8π ≈ 25.1327.
Sources: Perimeter — Wikipedia
Frequently asked questions
What is the difference between perimeter and area?
Perimeter measures the distance around a shape’s edge, in linear units. Area measures the surface it encloses, in square units. You use perimeter for fencing or framing, and area for flooring, paint or turf.
Why is a circle’s perimeter called circumference?
Circumference is just the special name for the perimeter of a circle. It equals 2πr, or equivalently π times the diameter, and represents the distance travelled going once around the circle.
How do I find the perimeter of an irregular shape?
Add up the lengths of every side, one by one. Perimeter is always the sum of all boundary segments, so an irregular polygon just needs each of its sides measured and totalled.
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This calculator is for educational purposes. Double-check important results before acting on them.