How it is calculated
The floor-to-floor height is divided by the preferred step height and rounded to a whole number of risers. The going follows the comfortable stride rule: two risers plus one going is about 63 cm. If space is limited, the going comes from the available length. The upper floor acts as the top step, so there is one tread fewer than risers.
Risers = height ÷ preferred step height, roundedComfortable stride: 2 × rise + going ≈ 60–65 cmAngle = arctan(rise ÷ going)Example
With 280 cm from floor to floor and steps of about 17 cm you get 16 risers of 175 mm and 15 treads with a 280 mm going. The stair takes 4.2 m of floor, its angle is 32° and the stringer is about 5 m long.
Tips from practice
- A comfortable stair angle is 30–37°. Steeper than 45° is hard to walk down.
- Make every step the same height: even 1 cm of difference makes people trip.
- Keep at least 2 m of headroom above the stair.
Questions and answers
What step height is comfortable?
150–180 mm. In homes 170–180 mm with a 270–300 mm going is most common.
How many steps for 3 metres?
With steps of about 17 cm, 18 risers of 16.7 cm.
What if there is not enough space?
Choose “Fit a given length”. If the angle goes above 42°, consider a turn or winder steps. Building rules in your country may set stricter limits.
Found a mistake in a formula? Write to [email protected]