How to Calculate the Pitch for Building Stairs

Determine what height the stair has to climb by measuring the distance from the bottom of the stairs to the top of the floor above. This measurement is your total rise. For example, 98 inches.

Determine the maximum run of the stairway. This is a good first estimate and will help you decide if need to make a turn in the stairway to reduce the steepness of the stairs. Measure the distance from one wall to another in the direction that the stairs will run. Subtract 6 feet for the two landings and what remains will be your run, for example, 17 feet wall-to-wall gives you an 11-foot run.

Determine the optimum run of the stairway. Divide the rise of the stairway by 7 inches; this is the optimum height of a step for the average person. You will eventually have to divide any remainder into the number of steps you will be using so that they are all of equal height, but to calculate the pitch you can just use the fraction. This number is one more than the number of steps in your stairway because the top landing serves as the final step. For example, a 98-inch rise divided by 7 inches is 14; after subtracting 1 you will have 13 steps in the optimal run. Multiply this amount by the normal tread depth of 10 inches to get the optimal run; in this case 130 inches.

Place the maximum run over the rise to arrive at the maximum pitch. Place the optimum run over the rise to determine the optimum pitch. At this point, you have enough information to determine if you will need an additional landing to turn the stairs safely to provide more run than the maximum straight stairwell allows. You want to be as close to the optimum pitch as possible. For example, with 98 inches of rise and 132 inches of maximum run the maximum pitch is 98/132. The optimum run is 130 inches giving the optimum pitch of 98/130. Since the optimum run is shorter than the maximum run, you can build the optimum run stairs and not use an additional landing.