Stair Calculator (Rise, Run & Stringer)
Design a staircase from the total rise: number of steps, riser height, tread depth, total run, stringer length and angle — checked against the IRC code limits.
How to use
- 1Measure the total rise from finished floor to finished floor.
- 2Enter the maximum riser height and tread depth you want (IRC: risers ≤ 7¾ in, treads ≥ 10 in).
How it's calculated
Risers = ⌈total rise ÷ max riser⌉; riser height = total rise ÷ risers. Treads = risers − 1. Total run = treads × tread depth. Stringer = √(rise² + run²). Comfort check: 2 × riser + tread ≈ 24–25 in.
Frequently asked questions
What are the code limits for residential stairs?
The US International Residential Code allows a maximum riser of 7¾ in and a minimum tread of 10 in, with variation between steps under ⅜ in.
Why is there one fewer tread than risers?
The top 'step' is the upper floor itself, so a staircase with 14 risers has 13 treads.
What's the most comfortable stair?
Around a 7 in riser and 11 in tread; the 2R + T = 24–25 in rule matches a normal walking stride.