Calculators / Stairs
Stair Calculator
For a total rise of 9 ft (108 in), you need 14 risers of 7 11/16 in and 13 treads. With 10 in treads, the stairs run 10 ft 10 in and each stringer is 14 ft 1 in long. Enter your height below.
Plan your stairs
| Riser height, decimal | 7.714 in |
|---|---|
| Total run | 10 ft 10 in (130.0 in) |
| Stringer length | 14 ft 1 in |
| Stair angle | 39.7° |
| 2 risers + 1 tread | 25.4 in |
Meets the residential code limits: risers up to 7 3/4 in and treads of at least 10 in.
How much will it cost? Building a 12 × 16 ft raised wood deck with railing and stairs typically costs $15,340 with a contractor. Deck building cost in your state
How to calculate stairs
Risers: divide the total rise by the maximum riser height and round up. 108 in ÷ 7.75 in = 13.9, so you need 14 risers. Riser height: total rise ÷ risers = 108 ÷ 14 = 7.714 in, about 7 11/16 in.
Treads: one fewer than the risers, because the upper floor is the top step: 13 treads. Total run: treads × tread depth = 13 × 10 in = 130 in. Stringer: √(rise² + run²) = √(108² + 130²) = 169.0 in.
Comfort check: many carpenters aim for 2 risers + 1 tread of about 24 to 25 in. Steeper stairs come in under that; very shallow ones come in over it.
Stairs by total rise
7 3/4 in maximum riser and 10 in treads.
| Total rise | Risers | Riser height | Treads | Total run |
|---|---|---|---|---|
| 2 ft | 4 | 6 in | 3 | 2 ft 6 in |
| 2 ft 6 in | 4 | 7 1/2 in | 3 | 2 ft 6 in |
| 3 ft | 5 | 7 3/16 in | 4 | 3 ft 4 in |
| 4 ft | 7 | 6 7/8 in | 6 | 5 ft |
| 5 ft | 8 | 7 1/2 in | 7 | 5 ft 10 in |
| 6 ft | 10 | 7 3/16 in | 9 | 7 ft 6 in |
| 7 ft | 11 | 7 5/8 in | 10 | 8 ft 4 in |
| 8 ft | 13 | 7 3/8 in | 12 | 10 ft |
| 9 ft | 14 | 7 11/16 in | 13 | 10 ft 10 in |
| 10 ft | 16 | 7 1/2 in | 15 | 12 ft 6 in |
Code requirements for home stairs
The 2021 International Residential Code, which most U.S. states use with local changes, sets these limits (IRC section R311.7):
- Riser height: no more than 7 3/4 in, and no riser more than 3/8 in taller than the shortest in the same flight.
- Tread depth: at least 10 in, with the same 3/8 in limit between treads.
- Nosing: 3/4 to 1 1/4 in, not required when treads are at least 11 in deep.
- Width: at least 36 in clear above the handrail.
- Headroom: at least 6 ft 8 in.
- Handrail: on at least one side of any flight with four or more risers, 34 to 38 in high.
Check with your local building department: cities and states can amend these rules.
Common questions
How many steps do I need for 8 feet?
For a 96 in rise with a 7 3/4 in maximum riser, you need 13 risers of 7 3/8 in and 12 treads. With 10 in treads, the stairs run 10 ft.
Why is there one fewer tread than risers?
The floor at the top acts as the last step, so a flight with 14 risers has 13 treads.
How long should a stair stringer be?
At least the stringer length shown above, which is the diagonal of the total rise and total run. Buy the next longer standard board, because the cut at the top and bottom needs a little extra.
Do deck stairs follow the same rules?
Yes. Stairs attached to a house deck follow the same residential code limits. Measure the rise from the deck surface to the landing or ground at the bottom.
What if my riser height is not an even fraction?
That is normal. Divide the total rise evenly so every riser matches, and mark the stringer to the nearest 1/16 in. Keep all risers within 3/8 in of each other.
How we calculated this
The calculator uses the formulas shown above and the code limits in IRC section R311.7. We test it against 155 worked examples, checked with a separate program. Sources.
Results are for planning. Your building department has the final say on stair rules where you live.
Changelog
- : Published.
- : Formulas checked against 155 worked examples, verified with a separate program.
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