Perimeter Calculator

A perimeter calculator returns the total distance around a rectangle, circle, or triangle. A rectangle's perimeter is 2 × (length + width), a circle's is π × diameter, and a triangle's is the sum of its three sides. A 12 ft by 10 ft rectangle has a perimeter of 44 ft.

Last reviewed September 2026Method & sources Report an error

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Perimeter

44.00 ft

Breakdown
Perimeter	44.00 ft

How to Calculate Perimeter

A rectangle's perimeter is `2 × (length + width)`, which covers both pairs of opposite sides. A circle's perimeter (its circumference) is `π × diameter`. It uses the same constant as a circle's area, applied to the diameter directly instead of the radius squared. A triangle's perimeter is simply the sum of its three side lengths, with no special formula needed.

Example: 12 ft × 10 ft rectangular yard

A 12 ft × 10 ft rectangular yard: Perimeter: 2 × (12 + 10) = 44 ft A 10 ft diameter circular bed instead: π × 10 ≈ 31.42 ft. A triangular bed with sides of 5 ft, 6 ft, and 7 ft instead: 5 + 6 + 7 = 18 ft.

Perimeter: Compare Scenarios

Scenario	Perimeter
Small (8×8 ft garden bed)	32.00 ft
Medium (12×10 ft yard section)	44.00 ft
Large (20×15 ft fenced yard)	70.00 ft

What Is Perimeter?

A perimeter calculator adds up the total distance around a shape's outer edge. It is useful for fencing, edging, trim, gutter, or any material that runs along a boundary rather than covering a surface. This calculator handles the three most common shapes: rectangle, circle, and triangle.

Perimeter: Pros and Cons

Pros

Handles the three most common shapes (rectangle, circle, and triangle) in one calculator
Uses the exact formula for each shape rather than an approximation
A quick first step for any boundary-based material, such as fencing, edging, trim, or gutter

Cons

Doesn't handle an irregular or L-shaped boundary directly. Break it into straight rectangular segments (plus a circular or triangular section if needed), find each segment's length, and add them together
A circle's perimeter here is its full circumference. For an arc or partial curve, multiply the circumference by the fraction of the circle the arc actually covers
Doesn't check whether three entered triangle side lengths can actually form a valid triangle (the two shorter sides must add up to more than the longest side). Verify your measurements if the result looks off

Perimeter: What a Pro Checks

Before ordering fencing or edging for a triangular boundary, check that the three side lengths you measured can actually form a triangle. The two shorter sides need to add up to more than the longest one, or a measurement has an error somewhere.
For an arc or a partial curve rather than a full circle, multiply the circumference by the fraction of the circle that arc actually covers instead of using the full circumference.
Break an irregular or L-shaped boundary into straight rectangular segments (plus a circular or triangular section if needed), measure each segment, then add them together for the total.

Frequently Asked Questions

How do you calculate the perimeter of a rectangle?

Add the length and width together, then double it: `2 × (length + width)`. A 12 ft × 10 ft rectangle has a perimeter of 2 × (12 + 10) = 44 ft.

How do you calculate the perimeter of a circle?

Multiply the diameter by π (about 3.14159). This is also called the circumference. A 10 ft diameter circle has a circumference of π × 10 ≈ 31.42 ft.

How do you calculate the perimeter of a triangle?

Add up the lengths of all three sides. A triangle with sides of 5 ft, 6 ft, and 7 ft has a perimeter of 5 + 6 + 7 = 18 ft.

What's the difference between perimeter and area?

Perimeter is the total distance around a shape's outer edge, useful for boundary materials like fencing or trim. Area is the amount of surface a shape covers, useful for coverage materials like flooring or paint. See the Square Footage calculator for area.

How do I find the perimeter of an irregular shape?

Break it into simpler rectangular, circular, or triangular sections along its boundary, find the length of each section, then add them together for the total perimeter.

Measurement