Stair calculator: how many steps do I need?
14 risers
7.71 in each · 13 treads of 10 in · 10 ft 10 in total run · stringer 14 ft 1 in at 39.7° · for 108 in of total rise
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Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
14 risers
7.71 in each · 13 treads of 10 in · 10 ft 10 in total run · stringer 14 ft 1 in at 39.7°
Source: IRC 2021 §R311.7.5 (International Code Council), read October 1, 2026. Read the source
A total rise of 108 inches needs 14 risers of 7.71 inches each and 13 treads of 10 inches, a total run of 130 inches, because the 2021 IRC caps a riser at 7 3/4 inches and allows no tread under 10 inches.
A worked example
A 7 ft 3 in rise (87 in) up to a deck, with 11 in treads needs 12 risers of 7.25 in. 87 divided by 7.75 is 11.2, so 12 risers; 11 treads of 11 in make a 121 in run and a 149 in stringer at 35.7°.
What does the IRC require for residential stairs?
In the 2021 International Residential Code a riser can be no more than 7 3/4 inches high and a tread no less than 10 inches deep, measured nosing to nosing, and within one flight the tallest riser and the deepest tread can differ from the smallest by no more than 3/8 inch. Headroom is at least 6 feet 8 inches measured from the line of the nosings, a flight can rise at most 12 feet 7 inches before it needs a landing, and the stair is at least 36 inches wide above the handrail. Nosings project 3/4 to 1 1/4 inches unless the tread is 11 inches or deeper. These are the minimums of the model code; your state or city adopts a version of it and can tighten them.
What else it is called
A stair calculator is also searched as a stringer calculator, a step calculator or rise and run: same flight, same figures. Risers are the vertical faces you climb and treads are the boards you step on; the stringer is the notched board that carries both, and its length is what you buy.
Common sizes
| Total rise | Risers | Riser height | Treads | Total run | Stringer |
|---|---|---|---|---|---|
| 2 ft 0 in (24 in) | 4 | 6.00 in | 3 | 2 ft 6 in | 3 ft 2 in |
| 3 ft 0 in (36 in) | 5 | 7.20 in | 4 | 3 ft 4 in | 4 ft 6 in |
| 4 ft 0 in (48 in) | 7 | 6.86 in | 6 | 5 ft 0 in | 6 ft 5 in |
| 5 ft 0 in (60 in) | 8 | 7.50 in | 7 | 5 ft 10 in | 7 ft 8 in |
| 6 ft 0 in (72 in) | 10 | 7.20 in | 9 | 7 ft 6 in | 9 ft 7 in |
| 7 ft 0 in (84 in) | 11 | 7.64 in | 10 | 8 ft 4 in | 10 ft 11 in |
| 8 ft 0 in (96 in) | 13 | 7.38 in | 12 | 10 ft 0 in | 12 ft 10 in |
| 9 ft 0 in (108 in) | 14 | 7.71 in | 13 | 10 ft 10 in | 14 ft 1 in |
| 10 ft 0 in (120 in) | 16 | 7.50 in | 15 | 12 ft 6 in | 16 ft 0 in |
| 11 ft 0 in (132 in) | 18 | 7.33 in | 17 | 14 ft 2 in | 17 ft 11 in |
| 12 ft 0 in (144 in) | 19 | 7.58 in | 18 | 15 ft 0 in | 19 ft 3 in |
The fewest risers that keep each one at or under the 7 3/4 in IRC maximum, with 10 in treads. Treads are one fewer than risers because the top floor is the last step.
Where the numbers come from
- Riser, tread and headroom limits: 2021 International Residential Code, Section R311.7.5.1 (riser height not more than 7 3/4 inches, and the greatest riser in a flight not more than 3/8 inch over the smallest), R311.7.5.2 (tread depth not less than 10 inches, with the same 3/8 inch variation), R311.7.2 (headroom not less than 6 feet 8 inches) and R311.7.3 (no flight rises more than 12 feet 7 inches between landings). Read on the ICC public access site October 1, 2026. Source
- The count is arithmetic on that limit: risers = total rise ÷ 7.75, rounded up; each riser = total rise ÷ risers; treads = risers − 1, because the top floor is the last step; total run = treads × tread depth; the stringer is the hypotenuse of rise and run, Pythagoras again.
This lays out one straight flight between finished floors: measure the rise from finished floor to finished floor, not subfloor to subfloor. The top and bottom need a landing at least as wide as the stair, a flight that rises more than 12 ft 7 in needs one in the middle, and the state or city that adopted the IRC can amend any of these figures: the limit that counts is the one in your adopted code.
By Javier Miralles · Last updated . How this site is made.
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