Stair Calculator – Risers, Treads & Code

Stair design starts with the total rise - finished floor to finished floor, not slab to slab. Divide by a target riser between 17 and 19 cm, round to a whole number of risers, then recompute the exact riser height; the number of treads is risers minus one. The comfort rule 2R + T ≈ 61-64 cm keeps the geometry walkable, and IRC limits cap residential risers at 19.7 cm (7.75 in) with a 25.4 cm (10 in) minimum tread. Worked example: a 2.82 m rise gives 15 risers of 18.8 cm and 14 treads of 25.5 cm - an angle of 36.4° and a total run of 3.57 m. Landings become mandatory above 3.7 m of rise, and headroom must stay over 2 m the whole way.

1. 1

   Measure the space

   Record the total rise and tread target at the widest and longest points.

2. 2

   Enter the values

   Type the measurements into the calculator and select your units.

3. 3

   Apply the formula

   The tool computes Risers = Total Rise ÷ Riser Height; Comfort: 2R + T = 63 cm; IRC max R = 19.7 cm, min T = 25.4 cm for your inputs instantly.

4. 4

   Add waste and order

   Review the total with a 5-10% margin and round up to whole units.

• Using nominal as actual sizes

• Spacing joists too wide

• No ground-contact treatment