Stair Stringer Calculator
Measure the total rise from finished floor to finished floor, choose a target riser height and tread depth, and get the number of steps, exact riser height, total run and stringer length, with a check against the IRC limits.
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Result
Enter your numbers to see the result.
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The method
- Number of risers = total rise ÷ target riser height, rounded to the nearest whole number.
- Actual riser height = total rise ÷ number of risers (all risers must be equal; the IRC allows no more than 3/8 in. variation).
- Treads = risers − 1. Total run = treads × tread depth.
- Stringer length = √(rise² + run²), plus extra for the notch at each end.
IRC R311.7 limits: riser height 7-3/4 in. maximum; tread depth 10 in. minimum; headroom 6 ft 8 in. minimum. A common comfort check is that riser plus tread should be about 17 to 18 in., or 2 × riser + tread should be 24 to 25 in. Local codes may differ.
Worked example
A 108 in. rise with a 7.25 in. target is 14.9, so 15 risers at 7.2 in.. That makes 14 treads at 10.5 in. for a 147 in. (12 ft 3 in.) run, and a stringer about 182 in. long.
Frequently asked questions
What is the maximum riser height?
The International Residential Code limits riser height to 7-3/4 inches and requires tread depth of at least 10 inches. Some jurisdictions and commercial codes are stricter (7 in. riser, 11 in. tread).
How do I handle the top and bottom step?
The finished floor counts as the top tread. Subtract the thickness of your tread material from the first riser so every step ends up the same height after finishing.
Related calculators
This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.