Stair calculator
- Risers
- 13
- Riser height
- 200 mm
- Treads
- 12
- Total run
- 3000 mm
- Angle
- 38.7°
- 2R + G
- 650 mm
Results update as you type.
How the calculator works
It divides the floor-to-floor height into the fewest equal risers that stay at or under your maximum riser height. The number of treads is one fewer than the number of risers, because the upper floor forms the last step. Total run is treads × going, and the angle is tan⁻¹(riser ÷ going).
Code limits used for the check
| Rule | Max riser | Min going | Other | Source |
|---|---|---|---|---|
| UK Approved Document K (2013 edition), private stair, Table 1.1 | 220 mm (min 150 mm) | 220 mm (max 300 mm) | Pitch 42° max; 2R + G 550–700 mm; headroom 2.0 m (loft conversions 1.9 m at the center, 1.8 m at the side) | Approved Document K (GOV.UK PDF) |
| UK Approved Document K (2013 edition), utility stair, Table 1.1 | 190 mm (min 150 mm) | 250 mm (max 400 mm) | 2R + G 550–700 mm; up to 16 risers per flight in buildings other than dwellings and common areas of flats | Approved Document K (GOV.UK PDF) |
| UK Approved Document K (2013 edition), general access stair, Table 1.1 | 170 mm (min 150 mm) | 250 mm (max 400 mm) | 2R + G 550–700 mm; up to 12 risers per flight in buildings other than dwellings and common areas of flats (exceptionally 16 in small premises) | Approved Document K (GOV.UK PDF) |
| US 2018 International Residential Code (IRC), Section R311.7, dwellings | 7¾ in (196 mm) | 10 in (254 mm) | Riser and tread may vary by no more than ⅜ in within a flight; headroom 6 ft 8 in (2,032 mm); width at least 36 in (914 mm); handrail 34–38 in (864–965 mm) high where there are four or more risers | City of Twin Falls Building Department, 2018 Residential Stair Guide |
For the roof above a new stair, use the roof pitch calculator; for flooring, the room area calculator. Background reading: roof pitch angles explained.
Questions
What is the maximum stair rise in the UK?
For a private stair in a home in England, Approved Document K (2013 edition) allows a rise of 150 mm to 220 mm with a going of 220 mm to 300 mm, a pitch of no more than 42 degrees, and twice the rise plus the going between 550 mm and 700 mm.
What is the maximum riser height under the IRC?
The 2018 International Residential Code (Section R311.7.5) sets a maximum riser of 7¾ inches (196 mm) and a minimum tread depth of 10 inches (254 mm), with no more than ⅜ inch of variation within a flight. Check which edition and local amendments your jurisdiction has adopted.
How much headroom does a stair need?
Approved Document K (2013 edition) asks for at least 2.0 m (6 ft 6¾ in) above the pitch line, reduced to 1.9 m at the center and 1.8 m at the side for loft conversions where space is tight. The 2018 IRC asks for at least 6 feet 8 inches (2,032 mm). Check local regulations, which can differ.
Does this calculator replace building control approval?
No. It checks your numbers against the published limits shown on this page. Your local building department or building control body decides what is acceptable for your project.