Stair Calculator

Calculate stair riser height, tread count and stringer length to building code.

          ┌────┐
          │Trd │ ← tread depth (run)
      ┌───┘    │
      │ Riser  │ ← riser height
  ────┘        │
               ▲ Total Rise (floor to floor)
Measurements

Frequently Asked Questions

What is the standard riser height for stairs?

IRC (US International Residential Code) limits stair risers to a maximum of 7¾ inches (196mm) and minimum of 4 inches (102mm). The most comfortable riser height is 7–7½ inches. All risers in a staircase must be within ⅜ inch of each other. UK Building Regulations require risers of 155–220mm.

How do I calculate the number of steps I need?

Divide the total rise (floor-to-floor height in inches) by the desired riser height, round to the nearest whole number, then recalculate the actual riser height. Example: 9-foot ceiling = 108 inches ÷ 7.5 = 14.4 → round to 15 steps → actual riser = 108 ÷ 15 = 7.2 inches per step.

How long should a stair stringer be?

Stringer length = √(total rise² + total run²). This is the hypotenuse of the right triangle formed by the total vertical rise and total horizontal run. For 15 steps with 7.2" risers and 10" treads: rise = 108", run = 15 × 10 = 150". Stringer = √(108² + 150²) = √(11,664 + 22,500) = √34,164 ≈ 184.8 inches (15.4 feet). Add extra for top and bottom cuts.