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Work out how many steps a straight staircase needs, how tall each riser is and how deep each tread should be. Enter the height from floor to floor, press Calculate and check the pitch, total run, stringer length and stairwell opening against the UK Building Regulations.
Number Of Risers
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Check the box above. The result updates once it looks right.
| Risers | Rise | Going | Pitch | Run |
|---|
Every riser count that passes for this height and stair type. More risers give a gentler stair but need more floor space. Your layout is highlighted.
The result gives the number of risers and treads, the rise and going of each step, the total run, the pitch, how long the stairwell opening needs to be, and a cutting list: stringers, tread boards, riser boards and handrail. Every figure is checked against the Building Regulations, and a table lists the other riser counts that would also work.
Stair builders use a handful of words that are worth knowing before you order timber or talk to Building Control:
| Term | What it means |
|---|---|
| Total rise | The height from finished floor to finished floor that the stair climbs. |
| Rise | The height of one step, from the top of one tread to the top of the next. Every rise in a flight must be the same. |
| Going | The depth of one step measured on plan, from the edge (nosing) of one tread to the edge of the next. It is not the depth of the tread board, which is longer because of the nosing overhang. |
| Riser and tread | The riser is the upright board or the step up; the tread is the part you stand on. A straight flight always has one less tread than risers, because the top riser steps onto the landing. |
| Pitch | The angle of the stair, measured along the line through the nosings (the pitch line). |
| Total run (going) | The floor length taken up by the treads: number of treads × going. |
| Stringer | The long side boards that carry the treads and risers. |
In England, stairs are covered by Approved Document K, Protection from falling, collision and impact. Table 1.1 sets the rise and going for three categories of stair:
| Type of stair | Rise | Going | Other limits |
|---|---|---|---|
| Private stair | 150 to 220 mm | 220 to 300 mm | Pitch no steeper than 42° |
| Utility stair | 150 to 190 mm | 250 to 400 mm | Up to 16 risers in a flight |
| General access stair | 150 to 170 mm | 250 to 400 mm | Up to 12 risers in a flight |
A private stair is one used by a single home. Utility stairs are for escape, access for maintenance or places that are not used by the public, and general access stairs are those in shops, offices, flats' common parts and other buildings used by the public. For every type, twice the rise plus the going must be between 550 and 700 mm, and a stair with more than 36 risers in consecutive flights needs a change of direction of at least 30°. Wales, Scotland and Northern Ireland have their own rules, which are similar but not identical, so check with your local Building Control if you build outside England.
The steepest private stair the rules allow uses a 220 mm rise and a 220 mm going, but that is 45° and fails the 42° limit. In practice the steepest legal domestic stair is about 200 mm rise with a 223 mm going.
Most UK houses have a floor-to-floor height of between 2.4 and 2.8 metres, so a typical straight stair has 12 to 14 risers. The table shows what the calculator gives for a private stair with plenty of room:
| Floor to floor | Risers | Rise | Treads × going | Pitch | Total run |
|---|---|---|---|---|---|
| 2,400 mm | 12 | 200 mm | 11 × 223 mm | 41.9° | 2.45 m |
| 2,500 mm | 13 | 192.3 mm | 12 × 235 mm | 39.3° | 2.82 m |
| 2,600 mm | 13 | 200 mm | 12 × 223 mm | 41.9° | 2.68 m |
| 2,700 mm | 14 | 192.9 mm | 13 × 234 mm | 39.5° | 3.04 m |
| 2,800 mm | 14 | 200 mm | 13 × 223 mm | 41.9° | 2.90 m |
| 3,000 mm | 15 | 200 mm | 14 × 223 mm | 41.9° | 3.12 m |
These are compact layouts close to the steepest a house stair is allowed to be, which is what most builders aim for to save space. If you have more room, add a riser: the stair becomes gentler and easier to climb, which matters for children and older people. The Other Layouts table in the result shows each option.
People walk up stairs with a natural stride of about 620 mm. A step that is short and tall, or long and shallow, breaks that rhythm and makes trips more likely. That is why the regulations say that twice the rise plus the going (written 2R + G) must be between 550 and 700 mm.
The calculator aims for 620 mm. With a 200 mm rise, that gives a going of 220 mm, but the 42° limit for private stairs pushes it up to 223 mm. With a 175 mm rise, it gives 270 mm. If you enter a fixed space, the going is reduced to fit, and the result shows a red cross if the stair can no longer meet the limits.
Approved Document K asks for at least 2.0 m of clear headroom above the pitch line along the whole stair. For a loft conversion where there is not enough height, it accepts 1.9 m at the centre of the stair, reducing to 1.8 m at the side.
The headroom sets how long the hole in the upper floor, the stairwell opening, has to be. You enter the depth of the floor above, from the finished floor down to the ceiling (250 mm is typical for joists, boards and plasterboard), and the calculator finds where a line 2 m above the pitch line meets the underside of that floor. For a 41.9° stair, the opening needs to be about 2.5 m long; a gentler stair needs a longer opening. If your joists are deeper or the ceiling is lower, make the opening longer. Trimming an opening in a floor usually means doubled or engineered trimmer joists, so ask a structural engineer, and see our joist span calculator for the floor itself.
The calculator tries every whole number of risers that would give a rise inside the limits for your stair type. For each one it sets the going, checks it, and picks the layout whose rise is closest to a comfortable target: 195 mm for a private stair, 175 mm for a utility stair and 160 mm for a general access stair.
Rise = total rise ÷ risers · Treads = risers − 1 · Going = 620 − 2 × rise, kept within the limits
Run = treads × going · Pitch = tan⁻¹(rise ÷ going) · Pitch line = √(run² + total rise²)
Stairwell opening = (headroom + floor depth) ÷ tan(pitch) · Tread board = width × (going + nosing)
The going is rounded to whole millimetres without going below any limit. If you enter a number of risers, the calculator uses it and shows which rules it fails. Stringers and handrails are given as the pitch line plus about 300 mm for cutting the ends, and a handrail is listed for both sides when the stair is 1 m wide or more. The calculator is for straight flights only: winders, spiral stairs and alternating tread stairs for loft conversions have extra rules.
Most UK houses have a floor-to-floor height of 2.4 to 2.8 m, which gives 12 to 14 risers. A 2,600 mm height is usually 13 risers of 200 mm with 12 treads.
220 mm under Approved Document K, with a going of at least 220 mm. Because the pitch must not exceed 42°, the practical maximum is about 200 mm with a 223 mm going.
42° for a private stair in England. Utility and general access stairs are limited by their rise and going instead, which keeps them well below that.
At least 2.0 m above the pitch line. In a loft conversion, 1.9 m at the centre and 1.8 m at the side are accepted if the full height is not possible.
Measure from the finished floor at the bottom to the finished floor at the top, including flooring on both levels. Measure in a few places, because floors are rarely level.
No. The going is measured on plan from one nosing to the next. The tread board is longer, because it overhangs the riser below by the nosing.
For a typical house stair of about 42°, about 2.5 m, so that there is 2 m of headroom above the pitch line. A gentler stair or a deeper floor needs a longer opening.
Yes. A new or replacement staircase, or a change to an existing one, is building work that must meet Approved Document K and is checked by Building Control.
Rise, going, pitch, 2R + G, headroom, handrail and riser limits from Approved Document K (2013 edition incorporating 2013 amendments), Table 1.1 and paragraphs 1.1 to 1.36. Stairwell opening uses the headroom and floor depth you enter. Reviewed November 2026.