Stair Calculator
Enter your floor-to-floor height. Get the risers, treads and stringer cut.
100% in your browser - no upload, no sign-up.
Risers (steps)
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Each riser: -
Treads
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Total run
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Angle
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Stringer length
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Comfort (2 × riser + tread)
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✅ Comfortable and within common code limits (riser ≤ 7¾ in, tread ≥ 10 in, 2R + T ≈ 24–25 in).
⚠️ Buildable, but outside the comfort range - 2 × riser + tread should be about 24–25 in. Try a different riser or tread.
⛔ Outside common code limits - riser over 7¾ in or tread under 10 in. Adjust your riser or tread.
💡 These are planning numbers. Stair codes vary by country and locality - always confirm riser, tread and headroom against your local building code, and cut one test stringer before cutting the rest.
⚠️ Include new flooring in the rise - or one step ends up uneven.
How to use this stair calculator
- Measure the total rise - the finished floor-to-floor height - and enter it in inches.
- Set your target riser height (7–7.5 in is typical) and tread depth (10–11 in is typical).
- Read the riser count, exact riser height, total run and stringer length, and check the code and comfort status.
How stair rise and run are calculated
The number of risers is your total rise divided by a comfortable target riser, rounded to a whole number - because every riser in a flight must be equal. Dividing the total rise by that whole number gives the exact riser height each step must be. Treads always number one fewer than the risers, and the total run is the tread depth times the number of treads. The stringer length is the hypotenuse of the rise-and-run triangle, √(rise² + run²), and the stair angle is arctan(rise ÷ run). The status check uses widely-adopted IRC limits - a maximum 7¾ in riser and minimum 10 in tread - plus Blondel's comfort rule, 2 × riser + tread ≈ 24–25 in.
Frequently asked questions
- How many steps do I need for my staircase?
- Divide your total floor-to-floor rise by a comfortable riser height - about 7 to 7.5 inches - and round to the nearest whole number to get the riser count. For a 108-inch (9-foot) rise, 108 ÷ 7.5 ≈ 14 risers, giving 13 treads. Enter your rise above for the exact count and the even riser height it produces.
- What is the ideal riser and tread size?
- A common target is a riser of 7 to 7.5 inches with a tread of 10 to 11 inches. Most building codes cap the riser at 7¾ inches and require a tread of at least 10 inches. The comfort rule of thumb is that twice the riser plus the tread should total about 24 to 25 inches - the calculator flags any layout that falls outside these.
- How do I work out the stringer length?
- The stringer is the diagonal board that carries the steps, so its length is the hypotenuse of the total-rise and total-run triangle: √(rise² + run²). For a 108-inch rise and a 130-inch run the stringer works out to about 169 inches. Add extra length for the cuts at the top and bottom; the calculator gives you the theoretical diagonal to lay out from.
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