The brick mason’s ruler is a folding ruler that folds at about 8-inch increments. According to the Construction Zone website, folding rulers were the most common ruler used before the invention of the measuring tape. Today, they are used primarily by brick masons. A brick mason's ruler not only has the basic inch measurements of any ruler but also a brick-spacing rule that helps a mason mark courses while laying bricks.

Measure the brick on the inches side of the ruler. When measuring the brick, include the mortar in the measurement. For example, a brick that is 2 inches thick combined with a mortar that is 1/2 inch thick has a total thickness of 2 1/2 inches thick.

Keep a finger at the appropriate inch measurement as you turn the ruler over to the other side, where the brick mason’s measurement is labeled. Note the number where the measurement lands on the brick mason’s side of the ruler.

Find the red number next to the number in black on the brick mason side of the ruler. This is the number of “courses” the ruler measures. The brick mason’s ruler has sets of numbers 1 through 0 combined with a red number next to the black 1 through 0 numbers.

Multiply the courses number, or the small red number, by the original measurement in inches to obtain the measurement in inches from the original measurement and the courses measurement required. For example, if the original measurement is 2 1/2 inches and the courses number is 3, the measurement on the inches side of the ruler is 7 1/2 inches.