How this calculator works
A staircase has one more riser than it has treads, because the top of the stair is the upper floor. The number of risers is the floor to floor height divided by the rise you would like, rounded up, and each step then rises the floor to floor height divided by that number. The pitch of the stair is the angle whose tangent is the rise divided by the going. For a private stair, Approved Document K allows a rise of up to 220 mm, a going of at least 220 mm, a pitch of up to 42 degrees, and sets 2 × rise + going between 550 and 700 mm.
Worked example: a floor to floor height of 2,600 mm with a preferred rise of 190 mm needs 14 risers (2,600 ÷ 190 = 13.7, rounded up), each 185.7 mm, with 13 treads. With a going of 250 mm the pitch is 36.6° and 2 × rise + going is 621 mm, so it meets Part K. The stair is 3.25 m long on plan. At the steepest rise (220 mm) it has 12 risers of 216.7 mm, and a gentle 175 mm rise needs 15 risers of 173.3 mm. A going of 200 mm is too short for a private stair, and gives a pitch of 42.9°. A going of 280 mm lowers the pitch to 33.6°. A 3,000 mm floor to floor height needs 16 risers.
Steps for common floor to floor heights (190 mm rise, 250 mm going)
Number of steps, the rise, the pitch and the length of the stair.
| Floor to floor | Risers | Rise | Pitch | Length on plan |
|---|---|---|---|---|
| 2,400 mm | 13 | 184.6 mm | 36.4° | 3.00 m |
| 2,500 mm | 14 | 178.6 mm | 35.5° | 3.25 m |
| 2,600 mm | 14 | 185.7 mm | 36.6° | 3.25 m |
| 2,700 mm | 15 | 180.0 mm | 35.8° | 3.50 m |
| 2,800 mm | 15 | 186.7 mm | 36.7° | 3.50 m |
| 3,000 mm | 16 | 187.5 mm | 36.9° | 3.75 m |
Tips before you buy
- Measure from the finished floor below to the finished floor above, including the floor coverings and the floor structure.
- Every riser in a flight must be the same height, and every going the same depth. People trip on a step that is different from the others.
- A shallower rise and a deeper going make an easier stair, but take more room. The comfortable range is a rise of 170 to 190 mm and a going of 250 to 280 mm.
- Allow for the thickness of the top tread, since the top step is the upper floor and the bottom step is the first tread.
- Check the headroom: you need 2.0 m clear above the pitch line, at the lowest point, and that decides where the stair can go.
Tools & materials for this project
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Frequently asked questions
How many steps do I need for a staircase?
For a floor to floor height of 2,600 mm and a comfortable rise of about 190 mm, 14 risers (13 treads), each 185.7 mm. At the maximum rise of 220 mm it would be 12.
What is the maximum rise of a stair under the Building Regulations?
For a private stair in a house, the rise (the height of each step) can be at most 220 mm, and the going (the depth of the tread) at least 220 mm, with a maximum pitch of 42 degrees.
What is the 2R + G rule?
Twice the rise plus the going should be between 550 and 700 mm for a comfortable stair. A rise of 186 mm and a going of 250 mm make 621 mm.
How long is a staircase on plan?
The length is the number of treads times the going: 13 treads of 250 mm make 3.25 m for this stair, plus any landing.
How much headroom does a staircase need?
At least 2.0 m of clear headroom above the pitch line (the line through the front edges of the treads), for the whole flight.
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