Stairs Calculator
Enter the floor-to-floor height and the calculator will size the steps and check them for comfort.
The comfort formula
Blondel's rule: 2h + b = 600–640 mm, where h is the riser and b the tread depth. It matches the length of a human stride: a smaller sum makes the steps fussy, a larger one forces you to stretch.
Worked example
A floor height of 2,800 mm with a preferred 175 mm riser: 2800 ÷ 175 = 16 steps of 175 mm. A 280 mm tread gives 2 × 175 + 280 = 630 mm, inside the comfortable range. The flight takes 15 × 280 = 4.2 m of floor.
Comfortable limits
| Parameter | Comfortable | Limit |
|---|---|---|
| Riser | 150–180 mm | up to 200 mm |
| Tread depth | 280–320 mm | from 250 mm |
| Pitch | 30–37° | up to 45° |
| Flight width | from 900 mm | from 800 mm |
What you must not do
- Mix step heights in one flight. The foot learns the rhythm by the second step, and an odd step is a classic cause of falls. A difference over 5 mm is already noticeable.
- Measure from the finished floor below but the subfloor above. Take the height between finished floor levels, including the screed and covering still to come.
- Forget headroom. Every step needs at least 1.9–2 m of clear height to the structure above.
Public buildings have their own regulatory requirements. This calculator is for private homes.
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