A good stair is one that you do not notice. People climb it without watching their feet, a tray of tea can be carried up it, and it is safe to come down in the dark. That comes from a few numbers being in the right relationship: the riser (the height of one step), the tread or going (its depth) and the pitch (the steepness of the whole flight).

Start with the floor-to-floor height

Measure from finished floor to finished floor. Divide it by the riser height you would like to get the number of risers, and round up to a whole number. Then divide the height by that whole number to get the actual riser, which is the same for every step.

For a floor-to-floor height of 3,000 mm and a maximum riser of 175 mm, 3,000 ÷ 175 = 17.1, so you need 18 risers. The actual riser is 3,000 ÷ 18 = 166.7 mm. Using 17 risers would make each riser 176.5 mm, which is more than the maximum.

Number of treads

A straight flight has one tread fewer than it has risers, because the floor at the top is the last step. With 18 risers and a tread of 275 mm, the flight has 17 treads and a total going of 17 × 275 = 4,675 mm. The pitch is the angle of the stair: arctan(166.7 ÷ 275) is about 31.2°.

The 2R + T rule

A long-used rule of thumb, often named after the French engineer Blondel, says that twice the riser plus the tread should be about 600 to 650 mm. In the example, 2 × 166.7 + 275 = 608 mm, which is comfortable. If the riser is high and the tread short, the stair is steep and tiring; if the tread is long and the riser low, the stride is awkwardly long. The rule helps you to choose a pair of numbers; it does not replace the code.

What codes usually specify

  • A maximum riser and a minimum tread. As one example, the US International Residential Code allows a riser of up to 7¾ in (about 196 mm) and needs a tread of at least 10 in (254 mm). Other countries and building types set other limits, and public buildings are stricter than houses.
  • A minimum clear width for the flight and the landings.
  • A minimum headroom, often around 2,000 mm or more, measured from the line of the nosings.
  • Handrails on one or both sides and their height.
  • A maximum number of risers in one flight before a landing is required.
  • Uniform risers. A variation of even a few millimetres between steps is a trip hazard and is limited by codes.

Landings and turns

A half landing or quarter landing breaks a long flight into two, which saves floor length and gives a place to rest. In a dog-leg stair the two flights run in opposite directions with a landing between them. A landing should be at least as wide as the stair so that people can turn.

Try it

The Staircase Calculator takes the floor-to-floor height, the maximum riser and the tread, and gives you the number of risers, the riser height, the number of treads, the pitch and the 2R + T value, with a section drawing. Use it to compare options quickly, then check the result against the code that applies to your building.

For ramps, the same approach works with a gradient instead of a riser and tread: the Ramp Calculator gives the length, the angle and the landings from the rise and the gradient.