How to use this calculator
- Choose the rules for where you live.
- Measure the total rise from finished floor to finished floor (include carpet, tiles or boards).
- Enter the tread depth you want.
- The calculator picks the fewest steps that pass every rule, and shows other options.
The formula
Risers = total rise ÷ maximum riser, rounded up
Riser height = total rise ÷ risers
Treads = risers − 1 (the top floor is the last step)
Total run = treads × going
Angle = arctan(riser ÷ going)
US IRC R311.7.5: risers no more than 7¾ in and treads at least 10 in. UK Approved Document K (private stairs): rise up to 220 mm, going at least 220 mm, pitch up to 42°, and 2 × rise + going between 550 and 700 mm. Germany, DIN 18065 (homes with up to two dwellings): rise 140–200 mm, going 230–370 mm, 2 × rise + going 590–650 mm. Netherlands, Bbl: rise at most 188 mm, going at least 220 mm. France: the Blondel rule, 2 × rise + going of 600–640 mm.
Every riser in a flight must be the same height, so the total rise is divided equally. A comfortable stair usually has 2 × riser + going of about 600–640 mm (24–25 in).
Worked example
For a total rise of 2,640 mm with 225 mm treads, the fewest steps that meet every UK rule are 14 risers of 188.6 mm.
That gives 13 treads, a total run of 2,925 mm and an angle of 40°. Fewer, taller risers would make the stair steeper than the 42° limit — see "Other options" in the results.
Tips before you buy
- Measure the total rise in several places; floors are rarely perfectly level.
- Allow for the finished floor on both levels — adding tiles later changes the first and last riser.
- Check the space at the bottom: you need a clear landing in front of the first step.
Frequently asked questions
›What is the maximum riser height?
7¾ in (196 mm) under the US IRC, and 220 mm for private stairs under UK Approved Document K. Local rules may differ.
›What is a comfortable stair?
Most people find 2 × riser + going of about 600–640 mm comfortable — for example a 180 mm riser with a 250 mm going.
›Does this calculator design the stringers?
No. It gives the geometry only. Stringer size, fixings and structural checks must follow your building rules or an engineer.
Sources
- US: IRC R311.7.5 stair treads and risers
- Germany: DIN 18065 step dimensions (BauNetz Wissen)
- Netherlands: Bbl rules for stairs in new homes (Informatiepunt Leefomgeving)
- UK: Approved Document K (protection from falling, collision and impact)
Formulas last reviewed: September 29, 2026. How we check our formulas