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Stair calculator

Work out how many steps a staircase needs, and the rise and going of each one, from the floor-to-floor height and the space you have. It checks the result against the Approved Document K limits for houses in England and tells you plainly what fails.

New timber staircase with bare treads and risers, sawdust on the floor

Loft stairs are allowed less headroom where there is no room for the full 2 m.

Measure from the top of the finished lower floor to the top of the finished upper floor.

The level distance from the first riser to the front of the top landing.

Most UK stairs are 170–200 mm. The legal maximum is 220 mm; we keep to it whatever you enter.

The vertical gap from the sloping line of the step nosings up to the ceiling or beam above.

Your result

Number of risers

14

13 treads

Number of treads
13the top floor is the last tread
Rise of each step
185.7 mmallowed 150–220 mm
Going of each tread
230.8 mmallowed 220–300 mm
Pitch
38.8 °42° maximum
2 × rise + going
602.2 mmshould be 550–700 mm
Total run
3 mhorizontal length of the stair
Stringer length
3.97 malong the pitch line
Building regulations check
PassesApproved Document K
  • These are Approved Document K limits for a private stair in England. Wales and Scotland differ. Handrails (900–1000 mm high) and guarding are not checked here.

Add this to your project shopping list, then print it or take it to the merchant.

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How to use the stair calculator

  1. Under What kind of stair? pick a main stair in a house or a stair to a loft conversion. Loft stairs are allowed less headroom where there is no room for the full 2 m.
  2. Type in the Total rise (floor to floor). Measure from the top of the finished lower floor to the top of the finished upper floor.
  3. Type in the Space available for the stair (horizontal). That is the level distance from the first riser to the front of the top landing.
  4. Enter the Step height you would like (rise). A rise of about 170–200 mm is a common choice. The legal maximum is 220 mm, and we keep to it whatever you enter.
  5. Enter the Headroom over the stair, measured from the sloping line of the step nosings up to the ceiling or beam above.
  6. Read the steps and the Building regulations check, then tap Share link to send the result to your builder or joiner.

Why use this calculator

It checks the rules for you. Rise 150–220 mm, going 220–300 mm, pitch no more than 42°, 2 × rise + going between 550 and 700 mm, headroom and the length of the flight are all tested, and each failure comes with a plain message.

It works from your real space. You give it the height and the room you have, and it gives you the number of risers, an equal rise and an equal going, in millimetres. If your space is too short, it tells you how much room you need instead.

It shows its working. Under How we worked it out you can see every step with your own numbers, so you can check the maths or show it to your builder.

How we worked it out

Your numbers, step by step. This updates as you change the calculator.

  1. Risers = total rise ÷ the step height you want = 2,600 mm ÷ 190 mm = 13.7, so 14 risers (this keeps each rise between 150 and 220 mm)
  2. Rise of each step = 2,600 mm ÷ 14 = 185.7 mm
  3. Treads = risers − 1 = 13 (the top floor acts as the last step)
  4. Going of each tread = 3,000 mm ÷ 13 = 230.8 mm
  5. Pitch = tan⁻¹(rise ÷ going) = tan⁻¹(185.7 ÷ 230.8) = 38.8°
  6. 2 × rise + going = 2 × 185.7 + 230.8 = 602.2 mm (should be 550–700 mm)
  7. Total run = 13 treads × 230.8 mm = 3 m
  8. Stringer (pitch line) length = √(total rise² + total run²) = √(2.6² + 3²) = 3.97 m. Allow extra for the cuts at top and bottom.

The formula

The calculator works out the number of risers first, then the rise and the going.

  • Risers: total rise ÷ the step height you want, rounded to a whole number and moved up or down if needed to keep each rise between 150 and 220 mm. For 2,600 mm at 190 mm that is 13.7, so 14 risers.
  • Rise of each step: total rise ÷ risers. 2,600 ÷ 14 = 185.7 mm.
  • Treads: risers − 1, because the top floor acts as the last step. So 13 treads.
  • Going of each tread: the space ÷ treads, but never more than 300 mm. 3,000 ÷ 13 = 230.8 mm.
  • Pitch: tan⁻¹(rise ÷ going). tan⁻¹(185.7 ÷ 230.8) = 38.8°.
  • 2 × rise + going: 2 × 185.7 + 230.8 = 602 mm.
  • Total run: treads × going. Stringer length (the sloping board that carries the treads): √(total rise² + total run²). Here that is 3.97 m, before extra for the cuts at the top and bottom.

What we assume

  • The limits are the Approved Document K (2013 edition) figures for a private stair in England: rise 150–220 mm, going 220–300 mm, pitch no more than 42°, 2 × rise + going 550–700 mm, headroom at least 2 m, and no more than 36 risers before a change of direction. Check GOV.UK for the current version.
  • For a loft conversion the headroom can be 1.9 m on the centre line of the stair, falling to 1.8 m at the edge (half the stair width), but only where 2 m is not possible.
  • The stair is a straight flight with equal steps. Winders, tapered treads, spiral stairs and landings are not worked out.
  • Not checked: handrails (900–1000 mm high, both sides if the stair is 1,000 mm wide or more), guarding (900 mm in a house, needed where the drop is more than 600 mm) and the 100 mm gap rule.
  • Wales and Scotland differ from England. Nothing here is structural advice.

Tips

  • Measure to the finished floors, after boards, carpet or tiles. Every riser in a flight should be the same height, and a top or bottom step of a different height is a trip hazard. Approved Document K says rise and going must be consistent throughout a flight.
  • If the going comes out over 300 mm, you have more room than the stair needs. Lower the step height you want and you will get a gentler stair with more steps.
  • If the going is under 220 mm, the stair does not fit. You need more length, or a longer route such as a turn or a landing. Ask your builder or an architect which suits your house.
  • More than 36 risers without a change of direction is over the limit, so a very tall stair needs a landing and a turn.
  • Building control must approve new stairs where building regulations apply. Show your drawings to your council's building control team, or an approved inspector, before you buy timber.
  • This is a planning aid, not a design. How the stair is fixed and supported, and the opening in the floor above, are structural matters for a joiner or structural engineer.

FAQs

How do I work out the number of steps, rise and going of a staircase in mm?
Divide the floor-to-floor height by the rise you want and round to a whole number of risers. Then divide the total rise by that number to get the rise, and divide the horizontal space by the treads (risers minus 1) to get the going. For 2,600 mm and 3,000 mm that is 14 risers of 185.7 mm and 13 goings of 230.8 mm.
What are the building regulations (Approved Document K) for stair rise, going and pitch?
For a private stair in England the rise is 150–220 mm, the going 220–300 mm, the pitch no more than 42° and 2 × rise + going between 550 and 700 mm. Wales and Scotland have their own rules.
What is the maximum pitch of a staircase in the UK?
42° for a private stair in England. The limits work together: a 220 mm rise with a 220 mm going would be a 45° pitch, so it is over the limit even though each number is inside its own range.
What headroom do I need over a staircase?
At least 2 m, measured vertically from the sloping line of the step nosings. For a loft conversion where 2 m is not possible, the minimum is 1.9 m on the centre line of the stair, falling to 1.8 m at the edge.
What is the maximum gap between spindles, and how high is a handrail?
In a house, guarding to a stair must not let a 100 mm sphere through, so spindle gaps must be under 100 mm. Handrails are 900–1000 mm high, on both sides if the stair is 1,000 mm wide or more. This calculator does not check these, so read Approved Document K or ask building control.
Do I need building control approval for a new staircase?
Where building regulations apply, yes. A new or altered stair, such as one for a loft conversion, normally has to be approved by building control. Check with your council before you start.

Last reviewed: 6 November 2026 · How we calculate · Report an error