I have just found this on the internet a few times it out lines how to measure up for bricks needed the bottom part is very consistent on lots of sites
For an easy rule of thumb guide you should allow 60 bricks per square metre for the building of a single skin wall. This is known as a half brick wall and is shown in Diagram 1. The style is known as Stretcher Bond with only the long ‘Stretcher’ faces of the bricks visible.
When determining how many bricks are required you should first work out the area of the brickwork as follows:- Length of wall say 4m, height of wall say 0.5m, multiply the two figures together, 4m x 0.5m = 2 square metres. Square metres are often written as ‘m2’ or ‘sq.m’.
In the example above for a 2 square metre wall you will need to multiply 2 (area of brickwork) x 60 (number of bricks per square metre) = 120 bricks.
If you intend constructing a one brick thick solid wall, as shown in Diagram 2, then you should allow for 120 bricks per square metre. So for a one brick thick solid wall you will need 2 (area of brickwork) x 120 (number of bricks per square metre) = 240
bricks. The visible ends of bricks are known as ‘Headers’.
These figures do not allow for wastage or breakage, so it would be advisable to add a few extra to the order to make certain you do not run short. Normally 10%; extra should be sufficient.