How to use this calculator
- 1Choose the rules for where you live.
- 2Measure the total rise from finished floor to finished floor (include carpet, tiles or boards).
- 3Enter the tread depth you want.
- 4The calculator picks the fewest steps that pass every rule, and shows other options.
The formula
- 01Risers = total rise ÷ maximum riser, rounded up
- 02Riser height = total rise ÷ risers
- 03Treads = risers − 1 (the top floor is the last step)
- 04Total run = treads × going
- 05Angle = arctan(riser ÷ going)
US IRC R311.7.5: risers no more than 7¾ in and treads at least 10 in. UK Approved Document K, Table 1.1 (private stairs): rise 150–220 mm, going 220–300 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.
Australia, NCC Housing Provisions Table 11.2.2a (stairs other than spiral stairs): riser 115–190 mm, going 240–355 mm and 2 × riser + going 550–700 mm. India, National Building Code 2016 (Part 3, cl. 12.18.1): for one- or two-family homes the riser may be up to 190 mm and the tread down to 250 mm (150 mm and 300 mm for other buildings), with at most 12 risers in a flight. Pakistan has no single national rule: Karachi's building regulations ask for a riser of at most 7 in (18 cm) and a tread of at least 9 in (23 cm) in houses, and other cities have their own bye-laws.
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, 220 mm for private stairs under UK Approved Document K, 190 mm in Australia (NCC), 190 mm for homes under India's National Building Code and 7 in (178 mm) in Karachi. 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.
Also searched as: stair stringer calculatorstair rise and run calculatorstaircase calculatorstep calculator
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 (2013), Table 1.1 rise and going — private stair 150–220 mm rise, 220–300 mm going
- Australia: NCC 2022 Housing Provisions, Part 11.2.2 and Table 11.2.2a (riser and going dimensions)
- India: National Building Code 2016, Vol. 1, Part 3 cl. 12.18.1 and Part 4 cl. 4.4.2.4.3.1 (text published by Public.Resource.Org)
- Pakistan: Karachi Building & Town Planning Regulations 2002, reg. 9-8 staircases (SBCA)
Formulas last reviewed: September 30, 2026 ·How we check our formulas