Stair Calculator
Calculate rise and run for stairs. Determine the number of steps, stringer length, and exact riser height for deck or interior staircase building.
Dimensions
Standard max: ~7.75" (19.7cm)
Standard min: ~10" (25.4cm)
How to Calculate Stair Stringers
Building stairs requires precise math to ensure every step is the exact same height. If steps vary by even a fraction of an inch, it creates a trip hazard.
- Measure Total Rise: The vertical distance from the top of the finished lower floor to the top of the finished upper floor.
- Determine Riser Count: Divide the Total Rise by your desired riser height (typically 7.5"). Round to the nearest whole number.
- Calculate Exact Riser: Divide the Total Rise by the number of risers to get the exact height per step.
Standard Stair Codes (IRC)
Always check local building codes, but general International Residential Code (IRC) standards are:
- Max Riser Height: 7 ¾ inches (196 mm)
- Min Tread Depth: 10 inches (254 mm)
- Headroom: Minimum 6 feet 8 inches
Stringer Length vs. Total Run
- Total Run: The horizontal distance the stairs will cover along the floor. Calculated as
(Number of Steps - 1) × Tread Depth. - Stringer Length: The length of the board needed to cut the stairs. It is the diagonal (hypotenuse) of the rise and run triangle.
? Frequently Asked Questions
The top floor itself acts as the final tread. So if you have 14 risers (vertical steps), you only need 13 actual stair treads before stepping onto the landing.
The ideal angle for a standard staircase is between 30° and 37°. Steeper stairs are harder to climb, while shallower stairs take up too much floor space.
Codes typically require a landing if the total vertical rise exceeds 12 feet (approx 3.6 meters). You may need to split the flight into two sections.