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 β†’ Round up to 16 risers

Step 2: Calculate actual riser height 108 / 16 = 6.75 inches per riser (≀ 7.75 in βœ“)

Step 3: Calculate tread depth Using 17.5 βˆ’ riser: 17.5 βˆ’ 6.75 = 10.75 inches per tread (β‰₯ 10 in βœ“)

Step 4: Calculate total horizontal run Number of treads = risers βˆ’ 1 = 15 (the top landing is a floor, not a tread) Total run = 15 Γ— 10.75 = 161.25 inches = 13.4 feet

Stair Angle

Angle = arctan(Rise / Run) = arctan(6.75 / 10.75) = 32.1Β°

Comfortable stairs are generally between 30Β° and 37Β°.

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 otherβ€”even one step that's ΒΎ inch taller is a major trip hazard.

Use our stair calculator to find the perfect rise and run for any floor height.