Stair calculator
Work out how many steps a staircase needs, and the rise and going of each, checked against the building regulations' guidance.
Limits from Approved Document K, on GOV.UK.
Result
12 risers of 216.7 mm with a 255 mm going are within Approved Document K's guidance for a stair in a home.
- ✓ Within Rise of each step: 216.7mm, against 150mm to 220mm
- ✓ Within Going of each step: 255mm, against 220mm to 300mm
- ✓ Within Twice the rise plus the going: 688.3mm, against 550mm to 700mm
- ✓ Within Pitch: 40.4°, against at most 42°
| Pitch | 40.4° |
|---|---|
| Treads | 11 |
| Going of the whole flight | 2,805 mm |
| Risers | Rise of each | Going that works |
|---|---|---|
| 12 | 216.7 mm | 241 to 266 mm |
| 13 | 200 mm | 223 to 300 mm |
| 14 | 185.7 mm | 220 to 300 mm |
| 15 | 173.3 mm | 220 to 300 mm |
| 16 | 162.5 mm | 225 to 300 mm |
| 17 | 152.9 mm | 245 to 300 mm |
Show the workings
| Step | Sum | Answer |
|---|---|---|
| Rise of each step | 2,600mm ÷ 12 risers | 216.667 mm |
| Twice the rise plus the going | 2 × 216.7mm + 255mm | 688.333 mm |
| Pitch | tan⁻¹(216.7 ÷ 255) | 40.354 ° |
| Treads, one fewer than the risers | 12 − 1 | 11 treads |
| Going of the whole flight | 11 × 255mm | 2,805 mm |
What this leaves out or assumes
- The top riser goes up to the landing or floor, so a flight has one fewer tread than risers.
Where the figures come from
- Smallest rise of a step, private stair (in a home): 150 mm. Source: Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK). Checked 13 November 2026.
- Largest rise of a step, private stair (in a home): 220 mm. Source: Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK). Checked 13 November 2026.
- Smallest going of a step, private stair (in a home): 220 mm. Source: Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK). Checked 13 November 2026.
- Largest going of a step, private stair (in a home): 300 mm. Source: Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK). Checked 13 November 2026.
- Twice the rise plus the going: smallest: 550 mm. Source: Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK). Checked 13 November 2026.
- Twice the rise plus the going: largest: 700 mm. Source: Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK). Checked 13 November 2026.
- Steepest pitch of a private stair: 42 degrees. Source: Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK). Checked 13 November 2026.
How to work out stairs
- Measure from finished floor to finished floor. That is the total rise.
- Divide it by the most a single step may rise. For a stair in a home that is 220 mm. Round up: that is the fewest risers you can have.
- Divide the total rise by that number of risers to get the rise of each step.
- Choose a going so that twice the rise plus the going is between 550 mm and 700 mm, and the pitch is no more than 42°.
A flight has one fewer tread than risers, because the top riser steps up onto the landing or floor.
What this does not check
Approved Document K also covers headroom, width, handrails, guarding, landings and tapered treads. Headroom over a stair is at least 2 m, and a loft conversion can use less where there is not room. Our guide to the stair regulations lists them. Approved Documents are guidance: your building control body decides whether work meets the regulations.