Determine the brick size and course dimensions of each type of brick. Take 10 random bricks from at least 4 different packs. To calculate the mean height (course dimensions), stack 10 bricks on top of each other. Measure the height and divide this by 10. To calculate the mean length (brick size), lay out 10 bricks in a contiguous row. Measure the length and divide this by 10. Make a ruler of the calculated dimensions, so your stretcher bond runs in a straight course and to avoid the need to grinding into the bricks when finished.