How to Calculate Stair Rise and Run
Comfortable, code-compliant stairs follow specific rise-and-run ratios that feel natural to climb. Getting these calculations right matters both for safety and for building permit approval.
Key Terms
- Rise: The vertical height of each step
- Run: The horizontal depth of each tread
- Total rise: The total vertical distance from floor to floor
The Building Code Rules (IRC Standard)
- Maximum riser height: 7.75 inches
- Minimum tread depth: 10 inches
- The "7-11 rule" is a good guideline: rise + run should equal about 17–18 inches
Step-by-Step Calculation
Total floor-to-floor rise: 108 inches (9 feet)
Step 1: Find number of risers 108 / 7 = 15.4 → Round up to 16 risers
Step 2: Calculate actual riser height 108 / 16 = 6.75 inches per riser (≤ 7.75 in ✓)
Step 3: Calculate tread depth Using 17.5 − riser: 17.5 − 6.75 = 10.75 inches per tread (≥ 10 in ✓)
Step 4: Calculate total horizontal run Number of treads = risers − 1 = 15 (the top landing is a floor, not a tread) Total run = 15 × 10.75 = 161.25 inches = 13.4 feet
Stair Angle
Angle = arctan(Rise / Run) = arctan(6.75 / 10.75) = 32.1°
Comfortable stairs are generally between 30° and 37°.
Consistent Riser Height Is Critical
The biggest stair accident risk is inconsistent riser heights. All risers in a flight must be within 3/8 inch of each other—even one step that's ¾ inch taller is a major trip hazard.
Use our stair calculator to find the perfect rise and run for any floor height.