In this section we calculate the perimeters of various shapes. The perimeter of a circle is referred to as the 'circumference'.

The circumference, *C*, of a circle = 2*πr* or *πd* where *r* is the radius and *d* is the diameter of the circle.

Calculate the circumference of a circle with radius 8 cm.

Using the formula, *C* = 2*πr*, gives

C | = | 2 × π × 8 = 50.26548246 cm |

= | 50.3 cm (to 3 significant figures) |

The diagram shows a semicircle of diameter 12 cm.

Calculate the perimeter of the semicircle.

Length of curve | = | π × 12 ÷ 2 |

= | 18.84955592 cm |

Total perimeter | = | 12 + 18.84955592 |

= | 30.84955592 cm | |

= | 30.8 cm (to 3 significant figures) |

The diagram shows a shape that is made up of a rectangle, a triangle and a semicircle.

Calculate its perimeter.

Length of curve | = | π × 7 ÷ 2 |

= | 10.99557429 cm |

Total perimeter | = | 8 + 5 + 8 + 7 + 10.99557429 |

= | 38.99557429 cm | |

= | 39.0 cm (to 3 significant figures) |