How many steps do I need?
Divide the total rise by the largest riser you want and round up. For a 108 in rise with risers of no more than 7½ in, 108 ÷ 7.5 = 14.4, so you need 15 risers of 7.2 in each, with 14 treads. At 10½ in per tread the stairs run 147 in.
Worked example: a 108 in rise
- Risers: 108 ÷ 7.5 = 14.4, rounded up to 15.
- Riser height: 108 ÷ 15 = 7.2 in.
- Treads: one fewer than the risers = 14, because the top step is the upper floor.
- Total run: 14 × 10.5 = 147 in.
- Stringer length: √(108² + 147²) = 182.4 in.
Steps needed by total rise
With risers of no more than 7½ in and 10½ in treads.
| Total rise | Risers | Riser height | Treads | Total run |
|---|---|---|---|---|
| 24 in | 4 | 6 in | 3 | 31.5 in |
| 36 in | 5 | 7.2 in | 4 | 42 in |
| 48 in | 7 | 6.86 in | 6 | 63 in |
| 72 in | 10 | 7.2 in | 9 | 94.5 in |
| 96 in | 13 | 7.38 in | 12 | 126 in |
| 108 in | 15 | 7.2 in | 14 | 147 in |
| 120 in | 16 | 7.5 in | 15 | 157.5 in |
Residential stair code limits
Most US jurisdictions follow the International Residential Code (IRC), section R311.7. Local codes can be stricter, so check with your building department before you cut stringers.
| Dimension | IRC limit |
|---|---|
| Riser height | 7¾ in maximum |
| Tread depth | 10 in minimum, nosing to nosing |
| Variation in one flight | ⅜ in maximum between largest and smallest |
| Headroom | 6 ft 8 in minimum |
| Width | 36 in minimum |
| Handrail height | 34 to 38 in |
How the calculator works
Risers = total rise ÷ largest riser, rounded up
Riser height = total rise ÷ risers
Treads = risers − 1
Total run = treads × tread depth
Stringer length = √(total rise² + total run²)
A comfortable stair usually has riser + tread between 17 and 18 inches. The stringer length is measured along the nosing line; allow extra board length for the cuts at the top and bottom.
Frequently asked questions
How many steps for a 9 ft ceiling?
With 9 ft ceilings, the floor structure usually brings the total rise to roughly 118 to 121 in. At 120 in you need 16 risers of 7½ in. Always measure the actual rise before you plan the stairs.
What is the maximum riser height?
The IRC allows up to 7¾ in for residential stairs, with no more than ⅜ in variation between risers in one flight. Some states and cities use a lower limit.
Why is there one fewer tread than risers?
The top riser brings you up to the upper floor, which acts as the last step, so it does not need a tread of its own.
How long should stair stringers be?
Start with the stringer length from the calculator and allow extra for the cuts at the top and bottom. In the example above the stringer is 182.4 in, about 15 ft 2 in, so 16 ft boards are the shortest that work; lay it out on the board before you buy.
Sources
- Town of Timnath, 2018 Residential Stair Guide (IRC R311.7)
- Viewrail, Tread Depth and Risers