Stair Calculator

Work out the number of steps, riser height, total run and stringer length for a staircase.

Units	Imperial (ft, in)
Total rise (floor to floor)	106 in
Maximum riser height	7.75 in
Tread depth (going)	10 in

Units

Total rise (floor to floor)

Maximum riser height

IRC maximum 7¾ in; UK private stairs 220 mm.

Tread depth (going)

IRC minimum 10 in; UK private stairs at least 220 mm.

Risers

14 × 7.57 in

13 treads of 10 in; total run 10.83 ft, angle 37.1°. 2 × riser + tread = 25.1 in (comfortable range 60–65 cm / 24–25 in).

Treads: 13
Total run: 10.83 ft
Stringer length: 13.98 ft
Angle: 37.1°

Side view: 14 risers of 7.57 in, 13 treads of 10 in

About the Stair Calculator

Divide the total rise by the maximum riser height and round up to get the number of risers; every riser must be equal. There's one fewer tread than risers when the top step is the upper floor. Comfortable stairs satisfy 2 × riser + tread ≈ 600–650 mm (24–25 in). Check your local building code.

The formula

Risers = ⌈rise ÷ max riser⌉; run = (risers − 1) × tread; stringer = √(rise² + run²)

Worked example

Example: Risers = 15 × 8 in

Inputs: Units: Imperial (ft, in); Total rise (floor to floor): 120 in; Maximum riser height: 8.5 in; Tread depth (going): 11 in.
Formula: Risers = ⌈rise ÷ max riser⌉; run = (risers − 1) × tread; stringer = √(rise² + run²)
Result: Risers = 15 × 8 in
Treads: 14
Total run: 12.83 ft
Stringer length: 16.27 ft

Questions people ask

What are the US code limits?

The IRC sets a maximum riser of 7¾ in and minimum tread of 10 in for homes.

What about the UK?

Approved Document K: private stairs max rise 220 mm, min going 220 mm, max pitch 42°.