How to Figure Stair Treads

Measure the distance from the top of the floor landing to the bottom of the stairway. This becomes the rise of the stairs. Write down the rise in overall inches.

Divide the rise by 7, the maximum stair height used in most building codes. Round up the resulting number to the next whole number. This becomes the number of steps in the stairs. For example, if the rise is 72 inches, divide 72 by 7 to get 10.28. Round 10.28 up to the next whole number, 11. You will need 11 steps in the stairway.

Divide the rise of the stairs by the number of steps to get the height of each step. Continuing with the example, divide 72 by 11, which results in a height for each stair of 6.455 inches.

Determine the location of the last tread in the stairway. If the tread is to be at the level of the floor at the top of the stairs, no alteration to the measurements is needed. If the top tread will be one step below the landing, subtract one step from the equation before determining the height required for each step.

Extend your measuring tape from the back edge of the uppermost tread straight out to where the end of the final tread is at the bottom of the stairs. This is the run of the stairs. Divide the run by the number of treads to determine the width of each tread. If the stairway has a total run of 121 inches and there are 11 treads or steps, the width of each tread is 11 inches.

Measure the distance between the stringers with the tape measure. The stringers are considered the sides of the stairs. Stringers set between walls are measured wall to wall; stringers with an open side are measured to the outside of the open stringer, with 1 inch added for an overhang. This measurement is the length of each tread.