# Perimeters

The perimeter is the outer limit of a region that's bounded by line segments. The perimeter is the path around an area. The word comes from the Greek, where peri means "around" and meter means "measure."

### Perimeters of Polygons

The perimeter (P) equals the sum of all the sides (s).

P = s + s + s + s + ...

Square: Multiply one side by four.

Rectangle: Multiply the length by two, multiply the width by two, and then add the products.

Parallelogram: Multiply the length (long side) by two, multiply the short side by two, and then add the products.

Regular polygon: For regular polygons (polygons with equal sides), multiply the length of one side by the total number of sides. For example, multiply one side of a regular pentagon by five to determine the shape’s perimeter.

Irregular polygon: Add all the sides.

### Circumference of Circle

A circle doesn't have a perimeter - it has a circumference. The circumference, just like a perimeter, is the distance around the curved edge of a circle. The word comes from the Latin circumferentia, from circum ("around") and ferre ("to carry").

Circumference equals pi multiplied by the diameter.

Circumference = π × diameter

C = π × d

C = πd

C = 2πr