# Perimeter

Perimeter is the distance around a two-dimensional shape.

### Example: the perimeter of this rectangle is **7+3+7+3** = **20**

### Example: the perimeter of this regular pentagon is:

**3 + 3 + 3 + 3 + 3** = **5×3 = 15**

The perimeter of a circle is called the circumference: Circumference = 2π × radius |

## Perimeter Formulas

Triangle Perimeter = a + b + c |
||

Square Perimeter = 4 × a a = length of side |
||

Rectangle Perimeter = 2 × (a + b) |
||

Quadrilateral Perimeter = a + b + c + d |
||

Circle Circumference = 2πr r = radius |
||

Sector Perimeter = r(θ+2) r = radius θ = angle in radians |
||

Ellipse Perimeter = very hard! |

## Try It Yourself

images/perimeter-ruler.js

625,626,757,3225,758,759,760,3224,3226,3227