Stair Calculator
Your estimate
- Riser height
- 7 3/16 in7.2 in · 18.3 cm
- Total run
- 11 ft 8 in11.67 ft · 3.56 m
- Angle
- 35.75°
- Stringer length
- 14 ft 8 7/8 in14.73 ft · 4.49 m
- 2 × riser + tread
- 24 3/8 in24.4 in · 62 cm
- Code check
- OK
Enter the floor-to-floor height — get risers, treads and total run, checked against the building code.
Updated 2026-10-20 · Based on: IRC R311.7 (US) and DIN 18065 (metric).
How to use the Stair Calculator
- Measure the total rise from finished floor to finished floor.
- Set the maximum riser height (7¾ in by the US code, 7–7½ in feels comfortable).
- Set the tread depth (10 in minimum by IRC, 11 in is comfortable).
- Read the number of risers, exact riser height and the space the stairs need.
Formula
Risers = total rise ÷ max riser, rounded up. Riser height = total rise ÷ risers. Treads = risers − 1.
Total run = treads × tread depth. Stringer length = √(rise² + run²). Comfort rule: 2 × riser + tread ≈ 24–25 in (63 cm).
Worked example
With the values preset in the calculator above:
- Total rise (floor to floor)
- 9 ft
- Max riser height
- 7.5 in
- Tread depth
- 10 in
- Risers
- 15
- Riser height
- 7 3/16 in (7.2 in)
- Treads
- 14
- Total run
- 11 ft 8 in (11.67 ft)
- Angle
- 35.75°
Stair rise and run code (IRC)
- Maximum riser height 7¾ in; risers may vary by no more than ⅜ in.
- Minimum tread depth 10 in (with nosing ¾–1¼ in when treads are under 11 in).
- Minimum width 36 in; minimum headroom 6 ft 8 in.
- Handrail at 34–38 in on stairs with four or more risers.
How many steps for 9 ft?
A 9 ft (108 in) rise with a 7½ in target needs 15 risers of 7 3/16 in and 14 treads, taking 11 ft 8 in of floor space with 10 in treads.
Steps for common floor heights
| Total rise (floor to floor) (ft) | Risers | Riser height | Total run |
|---|---|---|---|
| 3 | 5 | 7 3/16 in | 3 ft 4 in |
| 4 | 7 | 6 7/8 in | 5 ft 0 in |
| 6 | 10 | 7 3/16 in | 7 ft 6 in |
| 8 | 13 | 7 3/8 in | 10 ft 0 in |
| 9 | 15 | 7 3/16 in | 11 ft 8 in |
| 10 | 16 | 7 1/2 in | 12 ft 6 in |
| 12 | 20 | 7 3/16 in | 15 ft 10 in |
Frequently asked questions
How do I calculate stairs?
Divide the total rise by your target riser height and round up to get the number of risers; divide the rise by that number for the exact riser height; treads = risers − 1.
What is the standard stair rise and run?
About 7–7¾ in rise and 10–11 in run in the US; 17–18 cm and 26–29 cm in Europe.
How steep should stairs be?
Between 30° and 37° is comfortable for house stairs; the code maximum works out near 37–38°.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.