Staircase Calculator
Calculate the number of steps, total run length, and stair angle from floor height and riser height.
Supports inches and centimeters.
Staircase calculation determines the number of steps (risers), the height of each step, and the horizontal depth of each tread to create stairs that are safe, comfortable, and code-compliant.
The Key Formulas:
Number of risers = Total rise / Ideal riser height (round to nearest whole number)
Actual riser height = Total rise / Number of risers
Tread depth (run) = 600 − (2 × riser height) [in mm — the “2R + T = 600” rule]
Code Requirements (IRC — US Residential):
| Measurement | Minimum | Maximum |
|---|---|---|
| Riser height | 100 mm (4 in) | 196 mm (7¾ in) |
| Tread depth | 254 mm (10 in) | No limit |
| Stair width | 914 mm (36 in) | No limit |
| Headroom | 2,032 mm (6 ft 8 in) | No limit |
Worked Example:
Floor-to-floor height: 2,700 mm (2.7 m). Target riser height: 175 mm.
- Number of risers: 2,700 / 175 = 15.43 → round to 15 risers
- Actual riser height: 2,700 / 15 = 180 mm (within code ✓)
- Tread depth: 600 − (2 × 180) = 240 mm (use 250–280 mm for comfort)
- Total horizontal run: 14 treads × 250 mm = 3,500 mm (3.5 m of floor space needed)
Note: There is always one fewer tread than riser (the floor is the final “tread”).
Practical Tips:
- All risers must be within 3/8 inch (9.5 mm) of each other — uneven risers cause falls
- The landing at top and bottom should be at least as wide as the stair width
- Use a stair gauge on a carpenter’s square to mark consistent riser and tread lines on the stringer