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Basics
Stair dimensions: riser, tread and headroom
Stairs that feel right follow a simple relationship between step height and depth. This guide explains the dimensions that make stairs comfortable and safe, and how to work them out for your floor height.
1. The parts of a stair
The rise is the total height from finished floor to finished floor. Each step has a riser (its height) and a tread (its depth, where you put your foot). The run is the total horizontal length, and the stringer is the sloping board that carries the steps.
2. Number of steps
Divide the total rise by a comfortable riser height, usually 16–18 cm, and round to a whole number. Then divide the rise by that number to get the exact riser. For 280 cm: 280 ÷ 17.5 = 16 risers of exactly 17.5 cm. A straight flight has one tread fewer than risers, because the top step is the upper floor.
3. Tread depth and Blondel's rule
A comfortable stair matches the length of a natural step: 2 × riser + tread ≈ 63 cm (about 25 in), within a range of about 60–65 cm. A 17.5 cm riser gives a tread of about 28 cm. Steeper stairs (higher risers, shorter treads) save space but are tiring and less safe. The Stair calculator applies this rule.
4. Building code limits
Codes differ by country, so check your local rules. As examples, the US International Residential Code allows a riser of at most 7¾ in (196 mm) and a tread of at least 10 in (254 mm). Many European rules allow up to 18–19 cm risers in homes. All risers in a flight must be equal; codes allow only a few millimeters of difference, because uneven steps cause falls. In Germany, DIN 18065 allows risers of 14–20 cm and treads of 23–37 cm in houses with up to two dwellings; in Spain, the CTE requires treads of at least 28 cm and risers of 13–18.5 cm on general-use stairs.
5. Headroom, width and handrails
Keep at least about 2 m (6 ft 8 in) of clear headroom measured vertically from the line of the step nosings. Home stairs are typically at least 80–90 cm wide. A handrail is usually required on at least one side, at about 85–95 cm above the nosings, and open sides need guards that a child cannot climb through.
6. Measure before you build
Measure the rise between the finished floor levels, including flooring still to be laid; forgetting the floor finish is a classic cause of a short first or last step. See How to measure a room for materials for measuring tips.
Common mistakes
- Measuring the rise before the floor finishes are added.
- Mixing risers of different heights in one flight.
- Making stairs too steep to save space.
- Too little headroom under a beam or upper floor.
- Leaving out the handrail.
Frequently asked questions
What is a comfortable riser height?
About 16–18 cm (6¼–7 in) for homes.
What is Blondel's rule?
Two risers plus one tread should be about 63 cm (25 in), matching a natural stride.
How deep should a stair tread be?
Usually 25–30 cm, so that the whole foot fits.
How much headroom does a stair need?
At least about 2 m (6 ft 8 in), measured vertically above the step nosings.
Can risers be different heights?
No. All risers in a flight should be equal; small differences cause trips.