Stair Calculator

Compute the number of steps, riser height, tread depth, total run and stringer length for a straight staircase. Enter the total rise and choose a target riser height within typical building code ranges (15–20 cm / 6–7.5 in).

Enter stair details

Units
In cm (or inches). Total vertical height from floor to floor.
In cm (or inches). Recommended 25–30 cm (10–12 in).
Leave blank to auto-select based on the total rise. Recommended 15–20 cm (6–7.5 in).

Enter total rise and tread, then press Calculate stairs.

Stair formulas

Number of steps ≈ total rise ÷ target riser height

Actual riser height = total rise ÷ number of steps

Total run = tread depth × (number of steps − 1)

Stringer length = √(rise² + run²)

Comfort rule: 2 × riser + tread ≈ 63–65 cm (25–25.5 in)

Typical code ranges

  • Riser height: 15–20 cm (6–7.5 in)
  • Tread depth (going): 25–30 cm (10–12 in)
  • Riser height differences between steps: < 6 mm (¼ in)
  • Stair width: at least 90 cm (36 in) for main stairs

Concrete Calculator

Concrete for stair footings and landings.

Square Footage Calculator

Landing and surrounding area.

Frequently asked questions

Because a staircase is a repeated motion. If one step is 2 cm taller than the others, it is a trip hazard — especially on the way down. Building codes typically require risers to be within 6 mm (¼ in) of each other.

An old rule of thumb says that a comfortable stair has 2 × riser + tread ≈ 63–65 cm (25–25.5 in). For example, an 18 cm riser with a 28 cm tread: 2 × 18 + 28 = 64 cm. That combination feels natural to most people.