Stair Calculator
Step count, riser height, and total run.
Inputs
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Formula
steps = ceil(total rise ÷ target riser); actual riser = rise ÷ steps; run = (steps − 1) × tread
Divide floor-to-floor rise by a target riser height and round up to whole steps so all risers are equal. Total horizontal run uses (n−1) treads — the top floor is the last riser, not a tread.
Worked example
2.7 m rise with 18 cm target risers needs 15 steps (actual riser 18 cm). At 28 cm treads, the stair run is 3.92 m — check against available plan depth before cutting stringers.
Where this can give the wrong answer
- Building codes often require 2R + T ≈ 63 cm and max riser ~19 cm — verify locally.
- Landing platforms aren't modelled — subtract landing depth from available run manually.
- Headroom clearance isn't checked — measure from tread nosing to ceiling slope.
FAQ
- The top step lands on the upper floor; you walk on (steps−1) treads. The final riser meets the landing.