UK stairs calculator, Approved Document K
Enter your floor to floor height and your going, pick the stair type, and this works out the riser count, the rise, the pitch and the 2R+G figure, then checks all four against Approved Document K. A private stair in a house is the default.
The four limits a stair has to satisfy
Approved Document K sets rise and going as a pair, not individually, and adds a combined rule on top. All of these have to be true at once.
| Stair type | Rise | Going | Max pitch |
|---|---|---|---|
| Private, in a single dwelling | 150 to 220mm | 220 to 300mm | 42 degrees |
| Utility | 150 to 190mm | 250 to 400mm | Not stated |
| General access | 150 to 170mm | 250 to 400mm | Not stated |
The fourth limit applies to all of them: twice the rise plus the going has to fall between 550mm and 700mm. It is the rule that makes a stair feel right underfoot, and it is the one most often missed, because a rise and a going can each sit inside their own range while the pair of them together does not.
Every rise in a flight must be equal and every going must be equal. A single odd step at the top or bottom is a trip hazard and it is not permitted.
Headroom, and the loft conversion relaxation
You need 2 metres of clear headroom measured vertically from the pitch line of the stair. That single requirement kills more loft conversions at design stage than anything else, which is why Approved Document K relaxes it for exactly that case: in a loft conversion where the full 2 metres cannot be achieved, 1.9 metres at the centre of the stair width and 1.8 metres at the side is acceptable.
It is a relaxation for loft conversions, not a general allowance. Do not apply it to a new build or to a stair on a lower floor.
Handrails and guarding, and the number everyone gets wrong
A handrail goes 900mm to 1000mm above the pitch line. A stair needs one on at least one side, and on both sides once it is 1000mm wide or more.
Guarding is where the published advice goes wrong most often. In a dwelling, guarding to stairs, landings, ramps and the edges of internal floors is 900mm. The 1100mm figure that circulates as the UK guarding height applies to external balconies and to the edges of roofs, not to the landing on your first floor. If you have specified a 1100mm balustrade around an internal void because a trade site told you to, you have not broken a rule, but you have designed something taller than it needs to be.
Wherever guarding is required in a building that children under five will use, it must not allow a 100mm sphere through any gap, and it must not be easily climbable. That is the rule that governs baluster spacing, and it is a sphere test rather than a simple centre to centre measurement.
What this calculator does not check
Geometry only. It says nothing about whether the stair works as a means of escape under Part B, whether the stringer and the trimmer can carry the load under Part A, or whether the opening you are cutting needs a structural calculation. A stair that passes every figure above can still be the wrong stair for the building.
Keep the job moving after the setting out
Built Simple handles the estimate, the programme and the crew from one place, on the phone in your pocket. Free to start.
Start free with Built SimpleFrequently Asked Questions
What is the maximum rise for a stair in a house? 220mm. Approved Document K allows a rise between 150mm and 220mm for a private stair, paired with a going between 220mm and 300mm, and a maximum pitch of 42 degrees.
What is the 2R plus G rule? Twice the rise plus the going has to be between 550mm and 700mm. It is a comfort rule, and a stair can meet the individual rise and going limits while still failing it, so check it separately.
How many steps can you have before a landing in a house? Approved Document K sets no maximum number of risers per flight for a private stair in a dwelling. The commonly quoted 16 riser limit applies to other stair types. Headroom, the opening size and the space available are usually what decide it.
What height should a stair handrail be in the UK? 900mm to 1000mm above the pitch line. One side is enough until the stair reaches 1000mm wide, at which point you need a handrail on both sides.
Is guarding 900mm or 1100mm? In a dwelling it is 900mm for stairs, landings, ramps and the edges of internal floors. 1100mm applies to external balconies and the edges of roofs. The 1100mm figure is widely and wrongly quoted for internal landings.
What headroom do I need over a loft conversion stair? 2 metres normally. Where that cannot be achieved in a loft conversion, 1.9 metres at the centre of the stair and 1.8 metres at the side is accepted. That relaxation is specific to loft conversions.
Related calculators and guides
- Approved Document K explained
- UK ramp calculator, Approved Document M
- UK roof pitch calculator
- All UK calculators
Sources
- Approved Document K, Protection from falling, collision and impact, 2013 edition, HM Government. Free under the Open Government Licence.
- Building Regulations 2010, Schedule 1, Part K.
