The Formula for the Perimeter of a Rectangle Is P = 2 (L + B)

How do you calculate perimeter?

Worked examples: Calculating the perimeter of regular shapes

The perimeter of a closed shape is the distance around the outside of it. Sometimes you have to measure this, but the perimeter of some regular shapes can be calculated if you know the correct formulas.

The formula for the perimeter of a rectangle is P = 2 (l + b).

What is the perimeter of this rectangle?

P = 2 (l + b)

Substitute the actual dimensions.

P = 2(600 + 300)

P = 1800mm

The formula for the perimeter of a square is P = 4s.

What is the perimeter of this square?

P = 4S

P = 4 x 500

P = 2000mm

The formula for the perimeter of a triangle is P = a + b + c.

P = a + b + c

P = 500 + 450 + 300

P = 1250mm

Perimeter problems

1.  You have to cut some pipe which will cover the sharp edges on a piece of rectangular plate. The plate is 1200mm long and 75mm wide. How much pipe will you need to cover all the edges?

2.  How long a piece of wire will you need to wrap once around a piece of square tube? Each side of the tube is 65mm.

3.  If you walk completely around the outside of a triangular garden bed with sides 25 metres, 32 metres and 7 metres, how far have you walked?

4.  A rectangular table top is 1.225m by 0.620m. If trim is $1.60 a metre, how much will it cost to buy trim to go around the edge of the table top?

5.  A workshop is 2.40m wide and 4.35 m long. What length of skirting board is needed for this room? You will not need skirting board for the doorway, which is 0.8m wide.

Check your responses with the answers below.

Answers

(1) 2550mm (2) 260mm (3) 64 m (4) $59.04 (5) 12.7 m

Activity sheet: How do you calculate perimeter? Page 2