Perimeter is the total distance around the outside of a shape. To find it, add the lengths of all the sides.
A rectangle has two pairs of equal sides. If it is 12 cm long and 5 cm wide, the perimeter is 12 + 5 + 12 + 5 = 34 cm. A quick way is to add one length and one width, then double: (12 + 5) × 2 = 34. Perimeter is a length, so it is measured in cm, not cm².
Worked example
Find the perimeter of a rectangle 15 cm long and 4 cm wide.
- Add one length and one width: 15 + 4 = 19.
- Double it: 19 × 2 = 38.
Answer:38 cm
Key words
- perimeter
- the distance around a shape
- side
- one straight edge
- double
- multiply by 2
Practise this
New questions every time.
Common Core-referenced: 3.MD.D.8