Stair Calculator
Lay out a straight staircase from the total rise. Get the number of risers and treads, the exact riser height, the total run, the stringer length and the stair angle.
- Riser height
- 7.71 in
- Treads
- 13 treads
- Total run
- 130 in (10.83 ft)
- Stringer length
- 169 in (14.08 ft)
- Stair angle
- 37.6°
How this calculator works
The total rise is divided by the maximum riser height and rounded up to get the number of risers. The rise is then divided evenly, so every step is the same height.
A straight stair has one less tread than risers, because the top step is the upper floor. The total run is the number of treads multiplied by the tread depth.
The stringer length is the hypotenuse of the rise and run: √(rise² + run²). Cut stringers from boards a little longer than this.
Example: 108 in floor-to-floor rise
- Risers: 108 ÷ 7.75 = 13.9, rounded up to 14.
- Riser height: 108 ÷ 14 = 7.71 in.
- Treads: 14 − 1 = 13; total run: 13 × 10 in = 130 in.
- Stringer: √(108² + 130²) = 169 in, about 14 ft 1 in.
Quick reference
| Total rise | Risers | Riser height | Total run |
|---|---|---|---|
| 36 in | 5 | 7.2 in | 40 in |
| 48 in | 7 | 6.86 in | 60 in |
| 96 in | 13 | 7.38 in | 120 in |
| 108 in | 14 | 7.71 in | 130 in |
| 120 in | 16 | 7.5 in | 150 in |
Tips before you buy
- Measure the total rise between finished floor surfaces, not subfloors — flooring thickness changes the riser height.
- All risers in a flight should be equal; codes typically allow only 3/8 in difference between the tallest and shortest.
- Most codes require a handrail on stairs with four or more risers. Check local requirements.
Frequently asked questions
What is the maximum stair riser height?
The US International Residential Code (IRC) limits risers to 7¾ inches and requires treads of at least 10 inches. Local codes may differ.
How many steps do I need for 8 feet?
With 8 ft (96 in) of rise and a maximum 7¾ in riser, you need 13 risers of about 7.38 in each and 12 treads.
How long should a stair stringer be?
Calculate √(total rise² + total run²). For 108 in of rise and 130 in of run, the stringer is about 169 in, so buy a 16 ft board.
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Last updated October 25, 2026