How to use it
- Measure the height from finished floor to finished floor, including the floor finishes on both levels.
- Enter the riser height you aim for (170–180 mm suits most houses) and the tread depth (going), usually 250–300 mm.
- Read the number of risers, the real riser height and the horizontal run the stair needs in plan.
Worked example
A floor-to-floor height of 2.80 m with a target riser of 175 mm gives 2.80 ÷ 0.175 = 16 risers of exactly 175 mm. A straight flight has one tread fewer than risers, so with a 280 mm going the run is 15 × 0.28 = 4.20 m. The comfort check is 2 × 175 + 280 = 630 mm, inside the 600–660 mm range.
The rules a good stair follows
The comfort formula 2R + T ≈ 630 mm matches the length of a normal stride. Keep every riser in a flight the same height; a single odd step is where people trip. Leave at least 2.0 m of headroom measured vertically above the nosings, and a handrail at about 900 mm. For a family house a clear width of 900 mm is comfortable; local building codes set the minimum.
Frequently asked questions
How many steps for a 9 ft ceiling?
A 9 ft ceiling with a 12 in floor structure gives about 10 ft (120 in) floor to floor. At a 7 in target that is 17 risers of 7.06 in each and 16 treads.
What is the best riser height?
Between 165 and 180 mm (6½–7 in) for homes. Lower risers with deeper treads are easier for children and older people.
How long is a staircase in plan?
The number of treads times the tread depth. 15 treads of 280 mm need 4.20 m, plus a landing at the top and bottom.