Perimeter Calculator

Perimeter is the total distance around the outside of a flat shape, and for a circle it is called the circumference. This calculator covers rectangles, squares, triangles, regular polygons, circles and semicircles. It shows the formula, keeps π exact where it appears, and checks each answer by adding the sides another way.

Try:

How to use the perimeter calculator

  1. Choose the shape.
  2. Enter its measurements.
  3. Press Calculate to see the perimeter and the formula.

Formula

Prectangle=2(l+w)P_{\text{rectangle}} = 2(l + w)
C=2πrC = 2\pi r

Worked example: Rectangle 8 × 5

  • Shape: Rectangle
  • Length: 8
  • Width: 5

✓ Answer checked

P=26P = 26
Step-by-step working (2 steps)

  1. Use the formula Perimeter

    Perimeter is the total distance around the outside.

    P=2(l+w)P = 2(l + w)

  2. Substitute

    Put in the measurements.

    2(8+5)=262(8 + 5) = 26
Formulas used
P=2(l+w)P = 2(l + w)
How this was checked
  • ✓ Adding the sides one at a time gives the same total.

Answer is in the same units as the lengths entered.

Frequently asked questions

What is the perimeter of an 8 by 5 rectangle?

2 × (8 + 5) = 26.

What is the difference between perimeter and area?

Perimeter is the distance around a shape; area is the space inside it.

How do I find the perimeter of a semicircle?

Add half the circumference, πr, to the diameter, 2r.

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