Perimeter Calculator

Perimeter

Formula Used

About Perimeter Calculator

What Is Perimeter?

Perimeter is the total distance around the outside of a two-dimensional shape. If you walked along every edge of a shape and measured the total distance, that is the perimeter. For circles, the perimeter is called circumference. Perimeter calculations are essential for fencing a yard, framing a picture, installing baseboards, calculating the length of trim needed for a room, determining how much ribbon to wrap around a gift, and countless other practical tasks.

Perimeter Formulas

Rectangle: P = 2(length + width). Square: P = 4 x side. Triangle: P = a + b + c (sum of all sides). Circle (Circumference): C = 2 x pi x radius = pi x diameter. Regular Polygon: P = number of sides x side length. For irregular shapes, add the length of every edge.

How to Use This Calculator

Select your shape, enter the required measurements, and click Calculate. The perimeter appears in your chosen unit. For irregular polygons, enter each side length individually. The calculator works with any unit system and shows the formula used for reference.

Frequently Asked Questions

What is the difference between perimeter and circumference?

Circumference is the specific term for the perimeter of a circle. They mean the same thing: the total distance around the shape. Circumference is only used for circles and ellipses.

Can two shapes have the same perimeter but different areas?

Yes. A 1x9 rectangle and a 4x6 rectangle both have perimeter 20, but areas of 9 and 24 respectively. A circle has the maximum area for any given perimeter.

How do I find the perimeter of an irregular shape?

Measure every side and add them all together. If some sides are curved, measure along the curve or approximate with straight segments. For property boundaries, a surveyor's measurements provide exact perimeter.