Perimeter is the total length around an enclosed space. For example if you were to measure the perimeter of your garden and each side was 3 metres the total perimeter of your garden is 3 metres + 3 metres + 3 metres + 3 metres = 12 metres. So the perimeter of the garden is 12 metres. (12m) The perimeter of a book might be 30 centimetres + 30 centimetres + 20 centimetres + 20 centimetres = 100 centimetres. So the perimeter of the book is 100 centimetres. (100cm) It is important to put the measurement that you are using, for example cm, m, km. Watch the video about perimeter and complete the exercise attached. Extra for experts: Can you measure the perimeter of some items at home? Take pictures and label them with the perimeter.