Stair calculator
Work out the number of steps, rise, going, pitch and string length for a straight stair, checked against Approved Document K.
Measured from finished floor level to finished floor level.
The calculator uses the fewest steps that keep every rise at or under this height.
Measured level, nosing to nosing.
Number of risers and stair width
Leave empty to use the maximum rise.
Clear width between walls, strings or upstands. Checked only for a general access stair, where Approved Document K asks for 1,200 mm in a building other than a dwelling.
Stair layout
- Risers
- 1211 treads: the upper floor is the last step
- Rise
- 217 mm
- Going
- 250 mm
- Total going
- 2,750 mm2.75 m
- String length
- 3,785 mm3.78 m on the diagonal, before the end cuts
- Pitch
- 40.91°
- 2R + G
- 683 mm
Checked against Approved Document K (England), private stair
- Rise from 150 mm to 220 mmThis stair: 217 mmPass
- Going from 220 mm to 300 mmThis stair: 250 mmPass
- 2R + G from 550 mm to 700 mmThis stair: 683 mmPass
- Pitch 42° or lessThis stair: 40.91°Pass
Straight flight only. The figures are for England; Wales, Scotland and Northern Ireland have their own guidance. Headroom, handrails, guarding and open risers are not checked.
Estimate only. Check the product label and the building regulations where you live before you buy or build.
Quick answer
Divide the total rise by the largest rise you accept and round up to get the number of risers, then divide the total rise by that number for the rise of each step. A 2,600 mm floor-to-floor height at the 220 mm limit for a private stair in England needs 12 risers of 216.7 mm. With 250 mm goings the 11 treads take 2,750 mm of floor, and the pitch is 40.91°, under the 42° maximum.
How to use the stair calculator
- Measure the total rise from finished floor level at the bottom to finished floor level at the top. If new flooring is still to go down, add its thickness first.
- Leave the maximum rise at 220 mm, the limit for a private stair in Approved Document K, or lower it for an easier stair. The calculator picks the fewest risers that keep every rise at or under it.
- Set the going: type it, choose Space available and type the length of floor you have, or choose the 2R + G rule and type a target.
- Read the risers, rise, going, total going, string length and pitch, then the pass or fail list. Choose General access stair for a stair that is not inside a single home, and open "Number of risers and stair width" to force a number of risers or to check the width.
How do you work out the rise and going of a stair?
Divide the total rise by the largest rise you accept and round up: that gives the fewest risers that keep every step within the limit. Then divide the total rise by that whole number to get the rise, so every step is the same height. Approved Document K asks for the rise and going to be consistent throughout a flight (paragraph 1.5).
A straight flight has one tread fewer than it has risers, because the upper floor is the last step. The total going is the number of treads times the going. The string length shown is the diagonal from the foot of the first riser to the edge of the upper floor; the board you cut it from has to be longer to allow for the cuts at each end. Pitch is the angle between the horizontal and a line through the nosings.
risers = total rise ÷ maximum rise, rounded uprise = total rise ÷ riserstreads = risers − 1going from the space available = total going available ÷ treadsgoing from the 2R + G rule = target − 2 × risetotal going = treads × goingstring length = √(total rise² + total going²)pitch = arctan(rise ÷ going)2R + G = 2 × rise + goingWhat are the rules for stair rise and going in England?
In England, Approved Document K (2013 edition) is the guidance for meeting the stair requirement of the Building Regulations 2010. A private stair is one used by a single dwelling; a general access stair is used by everyone in a building as the normal route between levels. Wales has its own Approved Document K, Scotland uses its building standards technical handbooks and Northern Ireland uses Technical Booklet H. Your building control body has the final say on a project, and a qualified professional should check any structural stair work.
| Requirement | Private stair | General access stair |
|---|---|---|
| Rise (Table 1.1) | 150 to 220 mm | 150 to 170 mm |
| Going (Table 1.1) | 220 to 300 mm | 250 to 400 mm |
| 2R + G (Table 1.1) | 550 to 700 mm | 550 to 700 mm |
| Pitch (Table 1.1) | 42° or less | No separate limit; 170 mm on a 250 mm going is 34.22° |
| Headroom (paragraphs 1.11 and 1.13) | 2 m; in a loft conversion, 1.9 m at the centre of the stair and 1.8 m at the side | 2 m |
| Width (paragraphs 1.15 and 1.16) | No general minimum; 900 mm for a stair within the entrance storey on a severely sloping plot | 1,200 mm between walls, strings or upstands; 1,000 mm between handrails |
| Risers in a flight (paragraphs 1.17 and 1.18) | Change direction after more than 36 risers in consecutive flights | 12 between landings, exceptionally 16 in small premises |
| Handrail (paragraphs 1.34 and 1.35) | 900 to 1,000 mm above the pitch line; on both sides if the stair is 1,000 mm or wider | 900 to 1,000 mm above the pitch line; on each side of the flights and landings |
| Open risers (paragraphs 1.6 and 1.9) | Allowed if treads overlap by at least 16 mm and a 100 mm sphere cannot pass through | Not allowed |
| Guarding (paragraphs 1.40 and 1.41) | Where the drop is more than 600 mm | Where there are two or more risers |
Table 1.1 also lists a utility stair (rise 150 to 190 mm, going 250 to 400 mm), which the calculator does not check. The 1,200 mm width is for buildings other than dwellings; the 12-riser limit also covers common areas in blocks of flats.
How many steps do I need for my floor-to-floor height?
Worked out with a 220 mm maximum rise and 250 mm goings, the values the calculator starts with. Every row passes all four private stair checks: rise, going, 2R + G and pitch.
| Total rise | Risers | Rise | Total going | Pitch | 2R + G |
|---|---|---|---|---|---|
| 2,200 mm | 10 | 220 mm | 2,250 mm | 41.35° | 690 mm |
| 2,300 mm | 11 | 209.1 mm | 2,500 mm | 39.91° | 668.2 mm |
| 2,400 mm | 11 | 218.2 mm | 2,500 mm | 41.11° | 686.4 mm |
| 2,500 mm | 12 | 208.3 mm | 2,750 mm | 39.81° | 666.7 mm |
| 2,600 mm | 12 | 216.7 mm | 2,750 mm | 40.91° | 683.3 mm |
| 2,700 mm | 13 | 207.7 mm | 3,000 mm | 39.72° | 665.4 mm |
| 2,800 mm | 13 | 215.4 mm | 3,000 mm | 40.75° | 680.8 mm |
| 2,900 mm | 14 | 207.1 mm | 3,250 mm | 39.64° | 664.3 mm |
| 3,000 mm | 14 | 214.3 mm | 3,250 mm | 40.60° | 678.6 mm |
Rise and 2R + G are rounded to 0.1 mm; the calculator shows whole millimetres. The number of treads is one fewer than the number of risers.
Worked examples
Stair in a house with a 2.6 m floor-to-floor height
The finished floors are 2,600 mm apart. At the 220 mm maximum rise, 2,600 ÷ 220 = 11.82, which rounds up to 12 risers. Each rise is 2,600 ÷ 12 = 216.67 mm, which the calculator shows as 217 mm.
With 250 mm goings, the 11 treads take 11 × 250 = 2,750 mm of floor. The string diagonal is √(2,600² + 2,750²) = 3,785 mm, the pitch is arctan(216.67 ÷ 250) = 40.91° and 2R + G is 683 mm, so all four private stair checks pass. Lowering the maximum rise to 190 mm gives 14 risers of 186 mm, 3,250 mm of total going and a 36.61° pitch: a shallower stair that needs 500 mm more floor.
Loft conversion stair that has to fit in 2.7 m
The new loft floor will be 2,400 mm above the landing below, and there is 2,700 mm of floor for the stair. Type 2400 as the total rise, choose Space available and type 2700. The calculator gives 11 risers of 218 mm and goings of 270 mm with a 38.94° pitch, but 2R + G is 706 mm, over the 700 mm limit, so that check fails.
Open "Number of risers and stair width" and type 12. The rise drops to 200 mm, each going becomes 2,700 ÷ 11 = 245 mm, 2R + G is 645 mm and the pitch is 39.17°: all four checks pass in the same space. Where a loft conversion cannot reach 2 m of headroom, Approved Document K accepts 1.9 m at the centre of the stair and 1.8 m at the side.
Why can a stair fail on pitch when the rise and going are both in range?
Because the 42° pitch limit for a private stair is tighter than the rise and going limits put together. A 220 mm rise is allowed and a 220 mm going is allowed, but together they make a 45° stair. At a 220 mm rise the going has to be at least 244.4 mm to stay at or under 42°; at a 200 mm rise, at least 222.2 mm.
The 2R + G rule limits the other end: a 220 mm rise with a 300 mm going is inside both ranges, but 2 × 220 + 300 = 740 mm, over the 700 mm maximum. The calculator checks all four at once, so a stair that shows four passes meets Table 1.1 for a private stair.
Questions
What is the maximum rise for a stair in a house in the UK?
In England, the maximum rise for a private stair is 220 mm, with a going of at least 220 mm and a pitch of no more than 42°, under Table 1.1 of Approved Document K. A general access stair is limited to a 170 mm rise and a 250 mm minimum going. Wales, Scotland and Northern Ireland publish their own guidance, so check it if you build there.
How many steps do I need for a 2.6 m floor-to-floor height?
A 2.6 m (2,600 mm) rise needs 12 risers of 216.7 mm at the 220 mm maximum: 2,600 ÷ 220 = 11.82 rounds up to 12. The stair has 11 treads, because the upper floor is the last step, so with 250 mm goings it takes 2,750 mm of floor. The pitch is 40.91°, inside the 42° limit.
What is the 2R + G rule for stairs?
Twice the rise plus the going should come to between 550 mm and 700 mm, according to the note to Table 1.1 of Approved Document K. A stair with a 216.7 mm rise and a 250 mm going gives 2 × 216.7 + 250 = 683 mm and passes. Choose the 2R + G rule in the calculator to type a target and get the going from it.
Is the going the same as the tread depth?
No. Approved Document K defines the going as the depth from front to back of a tread, less any overlap with the tread above, so it is measured nosing to nosing and a tread board can be deeper than the going. In a house, open-riser treads must overlap by at least 16 mm, and a 100 mm sphere must not pass through the gaps.
How much headroom does a staircase need?
Approved Document K asks for at least 2 m of headroom above the pitch line of a stair and above its landings. In a loft conversion where there is not enough space for 2 m, 1.9 m at the centre of the stair and 1.8 m at the side are acceptable. The calculator does not check headroom, so measure the opening above the stair separately.
When does a staircase need a handrail on both sides?
A stair that is 1,000 mm wide or wider needs a handrail on both sides under paragraph 1.34 of Approved Document K. The top of the handrail goes 900 mm to 1,000 mm above the pitch line or floor, and it can form the top of the guarding if the heights match. In a house, guarding is needed where the drop is more than 600 mm.
Sources
- GOV.UK, Ministry of Housing, Communities and Local Government, Protection from falling, collision and impact: Approved Document K (checked 19 October 2026)Approved Document K is statutory guidance for building regulation in England.
- GOV.UK, Approved Document K: protection from falling, collision and impact, 2013 edition (PDF) (checked 19 October 2026)Table 1.1 rise, going, 2R + G and 42° pitch; headroom, width, risers per flight, handrails, open risers, guarding and the definitions of going, rise and pitch.
- Welsh Government, Approved Document K: protection from falling, collision and impact (checked 19 October 2026)Wales publishes its own Approved Document K.
- Scottish Government, Building regulations: building standards technical handbooks (checked 19 October 2026)Scotland uses domestic and non-domestic technical handbooks, April 2026 editions.
- Building Control Northern Ireland, Technical Booklets (checked 19 October 2026)Technical Booklet H covers stairs, ramps, guarding and protection from impact.
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