Stair Stringer Calculator
Measure total rise from the finished floor at the bottom to the finished floor at the top. You get the number of risers, each riser height to 1/16, and the stringer layout.
Estimate only. The warnings use common IRC residential limits (riser up to 7 3/4 in, tread at least 10 in). Your local code, the inspector, and the plans decide. This is a layout aid, not legal or code advice.
Result
Fill in your numbers and hit Calculate.
How the math works
Risers = total rise / max riser, rounded up
Riser height = total rise / risers
Treads = risers - 1 (the top floor is the last step)
Total run = treads x tread depth
Stringer line length = square root of (total rise x total rise + total run x total run)
Angle = atan(riser / tread)
Bottom cut = riser - tread thickness (so the first step comes out the same height)Common IRC residential limits for most stairs in a house: risers no taller than 7 3/4 in, treads at least 10 in deep, and risers in one flight within 3/8 in of each other. Splitting the rise evenly keeps every riser the same. Codes change by town and by year, so ask your inspector.
Buy stringer stock longer than the line length so you have room for the top and bottom cuts. Need to turn 9' 0 1/2" into inches? Use the Tape Measure Calculator.
Worked examples
Real numbers, run through the same math the calculator uses. Tap a link to load it into the calculator.
How many stairs for a 108 inch total rise?
14 risers at 7 11/16" and 13 treads. At 10 inch treads the total run is 10' 10" and the stringer line length is about 14' 1".
108 / 7.75 max riser = 13.94, round up to 14 risers
108 / 14 = 7.714 in = 7 11/16" each
Treads = 14 - 1 = 13
Run = 13 x 10 = 130 in = 10' 10"
Stringer = square root of (108 x 108 + 130 x 130) = 169.0 in = 14' 1"How many steps for a deck that is 30 inches high?
4 risers at 7 1/2" and 3 treads. With 10 inch treads the run is 2' 6" and each stringer is about 3' 6 7/16" long. Cut the bottom riser to 6 1/2" for 1 inch treads.
30 / 7.75 = 3.87, round up to 4 risers
30 / 4 = 7.5 in each
Treads = 4 - 1 = 3, run = 3 x 10 = 30 in
Stringer = square root of (30 x 30 + 30 x 30) = 42.4 in = 3' 6 7/16"
Bottom cut = 7.5 - 1 = 6 1/2"What is the riser height for a 96 inch rise?
13 risers at 7 3/8" with 12 treads. At 10 inch treads that is a 10' 0" run and a stringer about 12' 9 11/16" long.
96 / 7.75 = 12.39, round up to 13 risers
96 / 13 = 7.385 in = 7 3/8"
Treads = 12, run = 12 x 10 = 120 in = 10' 0"
Stringer = square root of (96 x 96 + 120 x 120) = 153.7 in = 12' 9 11/16"Can I build stairs with 8 inch risers and 9 inch treads?
For a 96 inch rise the math gives 12 risers at 8", but the calculator flags both. 8 inches is over the common IRC residential max riser of 7 3/4", and 9 inches is under the 10 inch min tread. For a 96 inch rise, switch to 13 risers at 7 3/8" with 10 inch treads. Check your local code.
96 / 8 = 12 risers at 8" (over 7 3/4")
Treads 9" (under 10")
Fix: 96 / 7.75 = 12.39, round up to 13 risers at 7 3/8"Free weekly email
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