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Stairway Calculations

2-18. Stairway Calculations

To calculate the number and size of risers and treads for a given run, first divide the total rise by 7. If the total rise for a stairway is 7 feet 10 inches or 94 inches, the answer will be 13.43. Since there must be a whole number for risers, select the one closest to 13.43 (13) and divide it into the total rise.

94 inches divided by 13 = 7.23 or 7 l/4 inches
Number of riser = 13
Riser height = 7 1/4 inches

In a given stair run (see Figure 2-38 ), the number of treads will be one less than the number of risers. A 10 1/2-inch tread will be correct for the following example, and the total run would be calculated as follows:

Number of treads = 12
Total run = 10 1/2 inches x 12 treads = 126 inches or 10 feet 6 inches

The stairs will have--

13 risers each, 7 1/4 inches high.
12 treads each, 10 1/2 inches wide.
A total run of 10 feet and 6 inches.

Figure 2-38. Stair run

Curriculum design: David L. Heiserman
Publisher: SweetHaven Publishing Services