Staircase Calculator

How the calculation works

Enter the height the stairs must climb and, optionally, the number of steps or tread depth. The calculator determines the number of risers, riser height h and tread depth b using the Blondel rule and checks the recommended ranges.

Formula and assumptions

Number of risers N ≈ H ÷ ideal riser height (about 17 cm), rounded to a whole number; riser height h = H ÷ N. Blondel rule: 2h + b ≈ 60–66 cm. Recommendations in the app: h 15–19 cm, b 24–32 cm. For straight stairs the number of treads is N − 1. Stair rules and regulations differ by country and building use.

Worked example

Floor-to-floor height H = 280 cm: N = 280 ÷ 17 = 16.47 → 16 risers, h = 280 ÷ 16 = 17.5 cm. For 2h + b = 63 cm: b = 63 − 35 = 28 cm. Treads 16 − 1 = 15, horizontal run 15 × 28 = 420 cm. The calculator's length L also includes the last tread at upper-floor level: L = 16 × 28 = 448 cm.

More worked examples

• Floor height 260 cm: N = 260 ÷ 17 = 15.3 → 15 risers, h = 260 ÷ 15 = 17.3 cm. For 2h + b = 63 cm: b = 63 − 34.6 = 28.4 cm. Treads 15 − 1 = 14, horizontal length 14 × 28.4 ≈ 398 cm.
• Only 300 cm of length for a floor height of 300 cm: N = 300 ÷ 17 = 17.6 → 18 risers, h = 16.7 cm, 17 treads. That is only 300 ÷ 17 = 17.6 cm per tread, far below the recommended 24–32 cm, so a straight flight will not fit; choose a type with a turn or landing.

Typical riser counts by floor height

What affects real consumption

• Floor finishes change the real height of the first and last step.
• The available length for the stair and headroom.
• Stair and safety regulations for the type of building.

Common mistakes

• Measuring the height to the bare slab and forgetting the floor finish, which changes the real height of the first and last step.
• Counting treads equal to risers: a straight flight has one tread fewer than risers (N − 1), because the upper floor acts as the last tread.
• Making steps of unequal height; every riser in a flight should be the same, so divide the total height evenly.
• Not checking headroom above the stairs, or treating the Blondel rule as a legal requirement instead of a guideline.

Frequently asked questions

What is the Blondel rule?

An empirical formula 2h + b ≈ 60–66 cm linking riser height and tread depth so that walking is comfortable and safe.

Does the calculator replace a stair design?

No – it gives indicative dimensions; final dimensions and compliance with regulations must be confirmed by the designer.

How do I calculate a staircase with a 180° turn?

Choose a type with a 180° turn: two flights with a flat landing, or winder treads. The calculator subtracts the landing length from the available length and works out the steps for each flight; the landing should be at least as deep as the stair is wide.

How many steps are needed for a floor height of 280 cm?

About 16 risers of roughly 17.5 cm, which means 15 treads in a straight flight. The calculator rounds the number of risers to a whole number and adjusts the height.

What is a comfortable riser height and tread depth?

Most comfortable stairs have a riser of about 17–18 cm and a tread of 27–29 cm, which satisfies 2h + b ≈ 63 cm. The calculator treats 15–19 cm and 24–32 cm as the recommended ranges.

How do I calculate spiral, T-shaped and alternating tread stairs?

Spiral: for H = 280 cm, a 160 cm diameter and 360° the calculator picks 15 risers (h = 18.7 cm) and a 24.1 cm tread on the walking line. T-shaped: H = 280 cm and L = 568 cm with a 120 cm landing give a main flight of 8 and two side flights of 8 treads each (24 treads, plan 548 × 344 cm). Alternating tread: for H = 260 cm 12 risers of 21.7 cm, going 12.5 cm and a 60.1° slope – for attics and limited use only.

Related calculators

• Concrete
• Surface Areas
• Volume
• Angle and Slope Conversion

Guides

• How to Calculate Stairs: Number of Steps, Riser Height and Tread Depth