Stairs calculator
Stair stringer, tread, and riser calculator
Calculate the number of steps, riser height, tread depth, and stringer length for your stair project.
Stairs calculator
Stairs calculator result
Building code requirements
- Maximum riser height: 7-3/4 inches (IRC)
- Minimum tread depth: 10 inches (IRC)
- Minimum tread width: 36 inches for main stairs
- Handrail required: 4 or more steps
- Headroom: Minimum 6 feet 8 inches
The calculator aims for riser heights close to 7 inches, which is the most comfortable and code-compliant standard for most stairs.
Worked example
For example, for a 8-ft total rise over 10-ft total run, with 7-in riser height:
- Steps = 8 ÷ (7 ÷ 12) = 13.7 → 14 steps
- Actual riser height = 8 ÷ 14 = 0.571 ft = 6.86 in
- Tread depth = (10 × 12) ÷ 14 = 8.57 in
- Stringer length = √(8² + 10²) = 12.81 ft
- Building code typically requires risers 4-7.75 in and treads at least 10 in
Common mistakes
| Mistake | Why it matters |
|---|---|
| Not following local building codes | Most codes require risers between 4 and 7.75 inches and treads at least 10 inches deep |
| Making inconsistent riser heights | All risers must be within ⅜ in of each other — uneven steps are a tripping hazard |
| Forgetting to account for tread thickness | The actual tread cuts on the stringer need to subtract the tread material thickness |