Åk 6–9
3.1 Calculating Perimeter
Imagine that you are going to walk the side lines around a football pitch with the following measurements.

How far have you walked when you have gone around once?

You have walked:
60 m + 100 m + 60 m + 100 m = 320 m
This distance, 320 m, is the measurement of the perimeter.  Perimeter is the measure for how far it is around the side of a figure.

Here we see a rectangle with the sides a and b.  The perimeter, which we express as P, then becomes:

P = a + b + a + b =
= 2a + 2b = 2(a+ b)