Stair Calculator
Calculate rise, going, stair length and check against building regulations.
Please note: Material estimates for planning only. Always confirm quantities against your drawings, local building codes and supplier specifications before ordering. Structural work requires a qualified engineer.
What the Stair Calculator does
Stair design starts from the fixed total rise between floors. Because every riser in a flight must be exactly equal, the rise is divided by a whole number of risers and the actual riser height falls out of that — it will rarely equal your preferred figure exactly.
Formula
Risers = round(Total rise ÷ Preferred riser)Actual riser = Total rise ÷ RisersTreads = Risers − 1Total run = Treads × GoingPitch = arctan(Total rise ÷ Total run)Comfort rule: 2 × Riser + Going should be 550–700 mm
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Total rise (floor to floor) | number | Yes | Accepts more than 0. |
| Total rise (floor to floor) unit | one of 6 options | Yes | — |
| Preferred riser height | mm | Yes | Accepts 50 or more, up to 300. |
| Going (tread depth) | mm | Yes | Accepts 100 or more, up to 500. |
| Nosing overhang | mm | Optional | Accepts 0 or more. |
| Stair width | number | Yes | Accepts more than 0. |
| Stair width unit | one of 5 options | Yes | — |
How to use it
- Choose Total rise (floor to floor) unit and Stair width unit.
- Enter Total rise (floor to floor), Preferred riser height, Going (tread depth) and Stair width.
- Optionally add Nosing overhang.
- Select Calculate.
Worked example
A 2.7 m floor-to-floor rise with a 180 mm preferred riser and 250 mm going.
- Rise
- 2.7 m
- Riser
- 180 mm
- Going
- 250 mm
15 risers of exactly 180 mm, 14 treads, 3.5 m run, 37.6° pitch, 2R+G = 610 mm — all within limits.
Frequently asked questions
Why is there one fewer tread than riser?
The top riser lands on the upper floor, which serves as the final tread. A flight with 15 risers has 14 treads.
What is the 2R + G rule?
A comfort check dating back centuries: twice the riser plus the going should land between 550 and 700 mm. It reflects natural stride length.