Stair Calculator: Rise, Run and Risers
Enter the height from finished floor to finished floor and a going. The calculator picks the number of risers, works out the rise, the run and the pitch, and checks them against the Approved Document K limits for private stairs in England: a rise of 150 to 220 mm, a going of 220 to 300 mm, a pitch of no more than 42 degrees, and twice the rise plus the going between 550 and 700 mm.
Last checked 10/11/2026. Sources: Approved Document K, 2013 edition (Table 1.1: private stairs, rise 150 to 220 mm, going 220 to 300 mm, 2R + G 550 to 700 mm, 42° maximum pitch).
Guide
How the calculator works
Take a 2.6 m floor-to-floor height and a target rise of 175 mm. 2,600 ÷ 175 = 14.86, which rounds to 15 risers. Each is 2,600 ÷ 15 = 173.3 mm. A flight with 15 risers has 14 treads. At a 250 mm going the run is 14 × 250 = 3.5 m. The stringer is √(2.6² + 3.5²) = 4.36 m and the pitch is 34.7°. Twice the rise plus the going is 2 × 173.3 + 250 = 597 mm, inside 550 to 700 mm.
You can type your own number of risers instead. With 13 risers each is 200 mm, which is allowed for the rise. With 11 risers each is 236 mm, over the 220 mm limit.
The rules it checks, and where they come from
Table 1.1 of Approved Document K (2013 edition) gives a private stair a rise of 150 to 220 mm and a going of 220 to 300 mm, with a maximum pitch of 42 degrees. It also gives the normal relationship between rise and going: twice the rise plus the going should be between 550 and 700 mm. All steps in a flight should be the same. Headroom is 2 m. Source: the GOV.UK document linked below.
Approved Document K applies in England. Wales, Scotland and Northern Ireland have their own rules. The Building Safety Regulator has been gathering evidence on possible changes to the guidance on domestic stairs, so check GOV.UK for the current edition before you build.
A tight space
If space is short, a shorter going is tempting. At 200 mm the run falls to 2.8 m, but 200 mm is under the 220 mm minimum, the pitch rises to 40.9°, and twice the rise plus the going falls to 547 mm, below 550 mm. The calculator flags both. Put your space in the optional box and it tells you whether the run fits and by how much.
What it does not check
- Headroom above the stairs, handrail and guard heights, landings, winders and tapered treads, which all have their own rules.
- Structure: stringer size and spacing, fixings and the floor above. Ask a builder or engineer.
- Local amendments. Councils and states can be stricter than the national or model code, and a permit or inspection may be needed.
- Existing stairs. Old houses are sometimes allowed to differ; ask your building authority.
Common questions
What rise should I aim for?
Any rise between 150 and 220 mm is allowed if the going and the 2R + G rule are also met. Many people aim for 170 to 180 mm. Use the target box to try values.
Does the top step count as a tread?
No. A flight has one fewer tread than risers because the floor above is the last step. The calculator uses that.
Does this apply in Scotland or Wales?
The limits shown are England’s. Check the rules for Wales, Scotland or Northern Ireland, and the current edition of the document for England.
Why must every step be the same?
Approved Document K says rise and going should be consistent through a flight. The calculator divides the height into equal risers.
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