Stair Riser Calculator
Calculate the number of stairs, riser height, and tread depth for any total rise.
Meets building code requirements.
Stair construction must balance comfort, safety, and building code requirements. The two critical measurements are the riser height (vertical) and tread depth (horizontal).
Key formulas:
- Number of risers = Total rise / Desired riser height (round to nearest whole number)
- Actual riser height = Total rise / Number of risers
- Total run = (Number of risers − 1) × Tread depth
- Stringer length = √(Total rise² + Total run²)
Building code requirements (IRC - International Residential Code):
- Maximum riser height: 7.75 inches (196 mm)
- Minimum tread depth: 10 inches (254 mm)
- Riser variation: No more than 3/8 inch (9.5 mm) difference between tallest and shortest riser
- Minimum headroom: 6 feet 8 inches (2032 mm)
- Minimum stair width: 36 inches (914 mm)
The comfort rule: The “rule of 17-18” states that the riser height plus tread depth should equal 17 to 18 inches. For example: 7" riser + 11" tread = 18" (comfortable).
Another comfort formula is: 2 × Riser + Tread = 24 to 25 inches. This is widely used by architects and builders across Europe and North America.
Common comfortable dimensions:
- 7" riser with 11" tread (residential standard)
- 7.5" riser with 10" tread (steeper but code-compliant)
- 6" riser with 12" tread (gentle, ideal for elderly)
Stringer considerations: A standard 2×12 stringer works for most residential stairs. For runs over 13 risers, consider a landing or intermediate support.