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Stair Stringer Calculator
Last updated: May 31, 2026
Written by Blake Boege
A stair stringer calculator is a carpentry planning tool used to determine the dimensions of the structural boards (stringers) that support a staircase. It divides the total vertical rise by a target step rise to compute the total number of risers and treads, then calculates the actual rise, actual run, incline angle, and the exact stringer board length needed. This helps carpenters lay out and cut the sawtooth patterns accurately while meeting local building codes.
Find the lumber length and exact cut measurements for your stair stringers. Input your total vertical rise and horizontal run to determine the exact number of steps, individual riser heights, tread depths, and incline angle.
Quick Answer
Calculate the required lumber length, step counts, and rise/run cutting dimensions for a stair stringer based on your total rise and run.
Staircase Boundaries
Height from bottom floor to top landing surface.
Total horizontal distance the stairs will cover.
Standard comfortable rise is around 7 to 7.5 inches.
Minimum lumber board length
136 in
Recommend buying at least a 12 ft 2x12 board
Examples
80 in total rise, 110 in total run, 7.5 in target rise
11 risers at 7.27 in rise, 10 treads at 11 in run, 136 in stringer length
36 in total rise, 48 in total run, 7 in target rise
5 risers at 7.20 in rise, 4 treads at 12 in run, 60 in stringer length
100 in total rise, 130 in total run, 7.5 in target rise
13 risers at 7.69 in rise, 12 treads at 10.83 in run, 164 in stringer length
How it works
Stair stringer geometry uses the Pythagorean theorem to calculate the length of lumber required, alongside proportional division of the total rise and run to ensure uniform step heights:
Step Count (Risers):
Number of Risers (N) = Round(Total Rise ÷ Target Riser Height)
Step Dimensions:
Actual Step Rise = Total Rise ÷ N
Actual Step Run = Total Run ÷ (N − 1)
Stringer Length & Angle:
Stringer Length = √((Total Rise)² + (Total Run)²)
Incline Angle = Arctan(Total Rise ÷ Total Run) × (180 ÷ π)
Verify dimensions against your local building codes (e.g., maximum riser height of 7.75 inches and minimum tread depth of 10 inches under the IRC) before purchasing lumber or making cuts.
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Frequently asked questions
A stair stringer is the structural support board that runs along the sides of a staircase. Treads (the steps you walk on) and risers (the vertical boards between steps) are fastened to it. The stringer is cut in a sawtooth pattern to support the stair layout.
Divide the total vertical rise of the stairs by a target step rise (usually 7 to 7.5 inches) and round to the nearest whole number to find the number of risers. Then, divide the total rise by this number of risers to get the exact actual rise per step.
Under the International Residential Code (IRC), the maximum riser height is 7.75 inches and the minimum tread depth (run) is 10 inches. A common rule of thumb for comfortable stairs is that the sum of one rise and one run should be between 17 and 18 inches.
In a standard staircase layout, the top riser meets the edge of the upper landing or floor level directly. Because the upper landing acts as the top tread, you need one fewer physical wooden tread board than the total number of vertical rises.
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