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Stair calculator
Enter the finished floor-to-floor height. The calculator picks the number of risers and a going that meets the Building Regulations limits for a private stair, and shows each check.
- Risers / treads
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- Each rise
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- Going
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- Pitch
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- Total going (floor space)
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- Stringer length (approx.)
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For a straight private stair in a dwelling. Winders, loft conversions and common stairs have other rules.
The Part K rules for a house stair
In England, stairs are covered by Approved Document K. For a private stair (one serving a single dwelling) the main geometry limits are:
| Rule | Private stair |
|---|---|
| Rise of each step | 150–220 mm |
| Going of each step | 220–300 mm |
| Maximum pitch | 42° |
| 2 × rise + going | 550–700 mm |
| Headroom over the pitch line | 2.0 m (lower allowed in some loft conversions) |
All risers in a flight must be the same height, and all goings the same depth. Wales, Scotland and Northern Ireland have their own regulations with similar but not identical limits.
How the calculator works
- It divides the floor-to-floor height by the 220 mm maximum rise and rounds up to get the fewest risers allowed.
- Each rise is the total height divided by that number, so every step is equal.
- It picks the smallest going that keeps the pitch at or under 42° and 2R + G at or over 550 mm. A shorter going saves floor space.
- You can override the risers or going to try other layouts. Every check updates as you type.
Worked example: 2,600 mm floor to floor
2600 ÷ 220 = 11.8, so 12 risers of 216.7 mm. The going must be at least 241 mm to stay under 42°, giving a pitch of 41.96° and 2R + G of 674 mm. With 11 treads the stair takes 2.65 m of floor. Adding a 13th riser (200 mm each) with a 250 mm going gives a gentler 38.7° stair, at the cost of 3.0 m of floor.
Other things Building Control will check
- Handrails: at least one side if the stair is under 1 m wide, both sides if wider, at 900–1,000 mm above the pitch line.
- Guarding: balustrades at least 900 mm high, with no gap a 100 mm sphere can pass through.
- Open risers: treads must overlap by at least 16 mm and the gap must not let a 100 mm sphere through.
- Landings: clear, level landings at the top and bottom, at least as long as the stair is wide.
This tool is a design aid, not approval. Check your final design with Building Control, an approved inspector or your stair manufacturer before you order or build.
Questions
What is the maximum rise for a stair in a house?
220 mm per step for a private stair in England under Approved Document K, with a minimum going of 220 mm and a maximum pitch of 42°.
What is the 2R + G rule?
Twice the rise plus the going must be between 550 and 700 mm. It keeps steps comfortable: tall steps need shorter goings, shallow steps need longer ones.
How much space does a staircase take?
For a typical 2.6 m floor height, a straight stair takes about 2.6 to 3.0 m of floor length plus landings at each end.
Do loft conversion stairs follow the same rules?
Mostly, but headroom can be reduced to 1.9 m at the centre of the stair (1.8 m at the side) where there is not enough height. Space-saver stairs have their own rules.
Results are estimates for planning and ordering. Check quantities with your supplier and product data sheets, and anything structural or regulated with a qualified professional. See our terms.