Find the perimeter of any shape.
Pick a shape, type its dimensions, and see the perimeter, the formula with your own numbers, and a labeled diagram update as you go. Circle perimeter is the circumference.
Your shape
What the numbers mean
The same perimeter in other units
Your dimensions are treated as generic lengths in the unit you picked. Here is that perimeter expressed in other length units.
Result scorecard
Perimeter formula for every shape
The perimeter is the total distance around the outside edge. Add up every side, or use the shortcut formula below.
| Shape | Formula | Your result |
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How perimeter grows when you scale the shape
Multiply every length by a factor and the perimeter changes by the same factor. Double the size and the perimeter is twice as long.
| Scale | Longest side | Perimeter | Perimeter vs now |
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Perimeter, explained
What perimeter is
Perimeter is the total distance around the outside edge of a two dimensional shape. If you walked all the way around the boundary and back to where you started, the distance you covered is the perimeter. It is always a length, so it is measured in units like feet, meters, or inches, never in square units.
The most direct way to find any perimeter is to add up the length of every side. For shapes with equal or repeating sides, a shortcut formula saves time: a square is four equal sides so P = 4 times side, and a rectangle has two lengths plus two widths so P = 2 times (length + width). A circle has no straight sides, so its perimeter has its own name, the circumference, found with P = 2 times pi times radius.
How to measure and calculate it
Start by identifying the shape, then measure each side you need in the same unit. Mixing units is the most common mistake: keep everything in feet, or everything in meters, before you add. Enter your numbers above and the perimeter, the substituted formula, and a labeled diagram update instantly.
For a regular polygon, every side is equal, so you only need one side length and the count of sides: P = number of sides times side length. For an irregular shape there is no shortcut, you simply measure each side and total them. When a job is priced by the linear foot, such as fencing, trim, or edging, the perimeter is the exact number you buy against, and adding a small waste allowance on top is wise.
Common questions
What is the perimeter of a shape?
The perimeter is the total distance around the outside edge of a two dimensional shape. You find it by adding the lengths of all the sides, or by using a shortcut formula for regular shapes.
What is the formula for the perimeter of a rectangle?
For a rectangle, P = 2 times (length + width). You add the length and width, then double the result, because a rectangle has two lengths and two widths.
How do you find the perimeter of a circle?
The perimeter of a circle is called the circumference. The formula is P = 2 times pi times radius, where pi is about 3.14159. If you know the diameter instead, the circumference is pi times diameter.
What is the difference between perimeter and area?
Perimeter is the distance around the edge of a shape and is measured in length units like feet. Area is the space inside the shape and is measured in square units like square feet. They answer different questions and use different formulas.
How do you calculate the perimeter of a regular polygon?
A regular polygon has equal sides, so the perimeter is the number of sides multiplied by the length of one side: P = number of sides times side length. A regular hexagon with 5 inch sides has a perimeter of 30 inches.
What units is perimeter measured in?
Perimeter is always measured in single length units such as feet, meters, yards, inches, or centimeters. Keep every side in the same unit before adding them, and never use square units, which describe area instead.
Results are geometric estimates based on the dimensions you enter. Measure carefully and keep every length in the same unit before you calculate.