Stair calculator checked against Part K
Enter the floor to floor height, and the floor space you have if you know it, to get the number of risers, the rise and going of each step, the pitch and the 2R+G figure, each checked against Approved Document K for a private stair in a house. It is free, and your figures are saved on this device only.
- Risers, rise, going and pitch
- Pass or fail on each Part K rule
- Works from the space you actually have
Enter the total rise from finished floor to finished floor, in millimetres. The going and the space for the stair are both optional.
The working
| ✓ Rise per step (150 to 220mm) | 216.7 mm |
|---|---|
| ✓ Going (220 to 300mm) | 241 mm |
| ✓ Pitch (42° or less) | 42° |
| ✓ 2 × rise + going (550 to 700mm) | 674 mm |
Also needed: at least 2m headroom (less is allowed in some loft conversions), handrails and guarding. Building Control has the final say.
How the calculator sets out a flight
Every step in a flight must have the same rise. So the calculator starts from the total rise and divides it into the fewest risers that keep each one at or under 220mm, the maximum for a private stair. Then it finds the going.
A going you type in always wins. Leave it blank and enter the space for the stair, and it divides that space by the number of treads. Leave both blank and it suggests the shortest going that passes every rule: at least 220mm, enough for 2R+G to reach 550mm, and long enough to keep the pitch at or under 42°. If no going can pass with that many risers, it adds one. Each result is then checked against Approved Document K.
A straight flight has one fewer tread than risers, because the top step is the landing floor. The calculator opens on a 2,600mm floor to floor height with no going entered:
- Risers: 2,600 ÷ 220 = 11.8, rounded up to 12 risers.
- Rise per step: 2,600 ÷ 12 = 216.7mm. Under 220, so it passes.
- Going: for 42°, the going must be at least 216.7 ÷ tan 42° = 240.6mm, so 241mm. That is over the 220mm minimum.
- Pitch: inverse tangent of 216.7 ÷ 241 = 41.96°. Just under 42°.
- 2R+G: 2 × 216.7 + 241 = 674mm. Inside 550 to 700.
- Floor space: 11 treads × 241 = 2,651mm from the bottom riser to the top one.
The Part K rules for a private stair
A private stair is one used by the occupants of a single home. These are the figures from Approved Document K, the government's guidance for England on stairs, ramps and guarding. The calculator checks the first four; the rest are for you to build in.
Rise: 150mm to 220mm
Table 1.1. Measured from the top of one tread to the top of the next. Paragraph 1.5 asks for level treads, with the rise and going consistent through the whole flight.
Going: 220mm to 300mm
Table 1.1. Measured nosing to nosing on plan, not along the tread. For dwellings, note 2 to the table sets a minimum going of 280mm for external tapered steps and stairs that are part of the building.
Pitch: 42° maximum
Note 1 to Table 1.1. A stair can pass on rise and going and still fail here, which is why the going often has to be more than the 220mm minimum.
2R+G: 550mm to 700mm
Twice the rise plus the going. A note to Table 1.1 calls it the normal relationship between rise and going, and it keeps steps a comfortable stride.
Headroom: 2m
Measured straight up from the pitch line and landings (Diagram 1.3). Loft conversions get a reduced figure where there is not room (Diagram 1.4).
Open risers and handrails
Open risers need treads that overlap by 16mm and gaps a 100mm sphere cannot pass (paragraph 1.9). Handrails sit 900mm to 1,000mm above the pitch line, on both sides if the stair is 1,000mm or wider (paragraph 1.34).
Worked example: fitting a fixed space
Most stairs go into a space that is already set by a wall or a doorway. Say the same 2,600mm rise has 2,750mm of floor between where the bottom riser will sit and the landing edge. Leave the going blank and enter 2,750 as the space for the stair:
- Risers: still 12, at 216.7mm each.
- Going: 2,750 ÷ 11 treads = 250mm.
- Pitch: inverse tangent of 216.7 ÷ 250 = 40.9°. Passes.
- 2R+G: 433.3 + 250 = 683mm. Passes, though close to the 700mm top.
- One more riser: the calculator always starts from the fewest risers, so work this one by hand. 13 risers at 200mm in the same 2,750mm gives 12 treads of 229mm, a pitch of 41.1° and 2R+G of 629mm. Shallower steps, shorter treads, and still a pass. Compare the two and pick the one that feels better to walk.
Measure finished floor to finished floor
The total rise is the height from the finished floor at the bottom to the finished floor at the top. Measure it on site, not from drawings, and allow for whatever is still to go down. If the hall will get 20mm of tile and adhesive after the stair goes in, that bottom step loses 20mm, and every other step is 216.7mm. Approved Document K expects the rise to be consistent through a flight (paragraph 1.5), so plan for the finished levels now.
For the space for the stair, measure horizontally from where the face of the bottom riser will be to where the face of the top riser will be. Do not include the landing. Check the headroom over the whole flight at the same time: hold a tape upright on the line of the nosings and make sure there is 2m clear to the ceiling or the floor above.
Measure to the millimetre. A 10mm error spread over 12 risers is under a millimetre a step. The same 10mm in one step is a trip hazard.
Stairs for loft conversions
Loft stairs follow the same rise, going, pitch and 2R+G rules. The difference is headroom. Where there is not space for 2m, Approved Document K accepts 1.9m at the centre line of the stair, dropping to 1.8m at the side (Diagram 1.4). That is often what makes a dormer or a rooflight over the stair necessary.
If a conventional stair will not fit at all, two space-saving options are allowed, but only in a loft conversion. An alternating tread stair (paddle stair) may give access to only one habitable room, plus a bathroom and/or a WC if wanted, as long as that WC is not the only one in the home. Its rise is up to 220mm and its going at least 220mm, measured between alternate nosings, with handrails on both sides and 2m headroom (paragraphs 1.29 and 1.30). A fixed ladder with handrails on both sides may serve a loft conversion with one habitable room when a stair cannot fit without altering the existing space (paragraph 1.32). Retractable ladders are not accepted as a means of escape (paragraph 1.31).
What the calculator does not do
It works out one straight flight. Winders and other tapered treads have their own measuring rules in Approved Document K (paragraphs 1.25 to 1.27 and Diagram 1.9), and spiral and helical stairs are designed to BS 5395-2. It does not work out stringer lengths, tread thickness, nosing overlap or the width of the stair.
It checks the private stair figures only. Stairs in shops, offices and the common parts of blocks of flats have tighter limits: a general access stair, for example, is limited to a 170mm rise and needs at least a 250mm going.
Approved Document K applies in England. Wales, Scotland and Northern Ireland publish their own guidance, so check the local version if you work there. Either way, the building control body inspecting the work has the final say, and talking to it before the stair is ordered is cheaper than altering one after.
Quoting a new stair or a loft conversion? Put the measured rise and going on the written quote so the customer sees what was allowed for, and price the fitting days with the day rate calculator.
Common questions
What is the maximum rise for a step in the UK?
220mm for a private stair in a house, under Approved Document K in England. The minimum is 150mm.
What is the minimum going for stairs?
220mm for a private stair, and no more than 300mm. In practice the going is often longer than 220mm, because the pitch must also stay at or under 42°.
How many steps do I need for a 2.6m floor to floor height?
At least 12 risers of 216.7mm, which is 11 treads plus the landing. 13 risers of 200mm gives shallower steps, but it adds a tread, so at the same going it takes more floor.
What is the 2R+G rule for stairs?
Twice the rise plus the going should come to between 550mm and 700mm. A 200mm rise with a 250mm going gives 650mm.
What is the maximum pitch for a staircase?
42° for a private stair in a home. The calculator shows the pitch for your rise and going and flags anything steeper.
How much headroom do stairs need?
2m, measured vertically above the pitch line and landings. In a loft conversion without space for that, 1.9m at the centre of the stair and 1.8m at the side is accepted.
Can a house stair have open risers?
Yes, if the treads overlap by at least 16mm and a 100mm sphere cannot pass through the gaps.
How do I calculate stairs?
Divide the total rise by 220 and round up to get the risers. Divide the total rise by the risers to get each rise. Then pick a going that keeps the pitch at or under 42° and 2R+G between 550 and 700.
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