In order to get an accurate estimate of the number of bricks in a wall, divide the area of the wall by the area of an average brick. This will result in an estimate on the high side, unless the size of a typical mortar layer is factored into the average brick size as well.
To get the dimensions of a wall, examine the blueprints of the building. If that is not possible, it can be measured using a tape measure. The area can be calculated by using the area for a rectangle, which is the length times the width. After measuring the size of a single brick with a measuring tape or ruler, the brick area can be calculated similarly by multiplying width and length dimensions. Finally, dividing the wall area by the average brick size will give the approximate number of bricks.