Loona Construction Calculators
Designing a staircase or deck steps? Enter the total floor-to-floor rise and your tread depth, and the calculator chooses a step count, works out the exact riser height so every step is identical, the total run, and the stringer length — and checks the result against the classic comfort rule.
For homes, risers of 170–190 mm (about 7 in) with treads (goings) of 250–300 mm (10–12 in) feel natural. The exact combination matters less than the comfort rule: 2 × riser + tread ≈ 630 mm.
People climb stairs by rhythm, not by looking. A riser that differs by even 10 mm from the rest is a classic trip hazard — which is why the calculator divides the total rise into perfectly equal steps instead of using a fixed riser and a leftover.
From the finished floor level downstairs to the finished floor level upstairs — including flooring thickness at both ends. Measure twice at the stairwell opening; an error here spreads across every step.
Number of risers = Total rise ÷ Target riser (175 mm / 7 in), rounded to a whole number
Actual riser = Total rise ÷ Number of risers (identical for every step — this is the key to a safe stair)
Total run = Tread depth × (Risers − 1)
Stringer length = √(Total rise² + Total run²)
Comfort rule: 2 × Riser + Tread should be about 600–650 mm (24–25.5 in) — the length of a natural stride on stairs.
The stringer is the diagonal board (or steel section) that carries the treads. Its minimum length is the hypotenuse of rise and run; order longer than the calculated figure to allow for the end cuts and the connection details.
Building rules typically require at least 2 m (about 6 ft 8 in) of clear headroom above the stair line, measured vertically from the tread nosings. Check the stairwell opening length when you fix the run.
The calculator uses widely accepted design targets (riser ≈175 mm, comfort 600–650 mm), but maximum riser and minimum going limits differ by country and building type. Always confirm your design against your local building code before building.
Add this calculator to your own website or blog — it is completely free, needs no sign-up, and always shows the latest version. Copy the code below and paste it into your page where you want the calculator to appear. Keeping the small “Powered by Loona Automation” credit line under the embed helps keep this tool free — but you are free to style or remove it; the tool works either way.