# 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 |
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Square Perimeter = 4 × a a = length of side |
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Rectangle Perimeter = 2 × (a + b) |
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Quadrilateral Perimeter = a + b + c + d |
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Circle Circumference = 2πr r = radius |
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Sector Perimeter = r(θ+2) r = radius θ = angle in radians |
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Ellipse Perimeter = very hard! |

## Try It Yourself