How This Calculation Works
The staircase calculator uses the total floor-to-floor height and your desired riser height to determine the number of steps. It divides the total height by the desired riser to find the number of risers, then calculates the actual riser height (total height ÷ number of risers).
The number of treads is always one less than the number of risers (the floor at the top acts as the final tread). The total run is calculated by multiplying the number of treads by the tread depth.
The stringer length uses the Pythagorean theorem: √(total rise² + total run²). Building codes typically require risers between 178–200 mm (7–7¾ in) and treads no less than 254 mm (10 in).
Common Mistakes to Avoid
- Ignoring building codes. Most codes require risers between 178–200 mm. Going outside this range creates unsafe stairs.
- Measuring to the wrong floor. Measure from finished floor to finished floor, not subfloor to subfloor.
- Inconsistent risers. Even a 5 mm difference between risers is a trip hazard. Calculate carefully and cut precisely.
- Forgetting headroom. You need at least 2,032 mm (80 in) of clearance above each tread for safe passage.
Worked Example
Scenario: A floor-to-floor height of 2.7 m with a desired riser height of 180 mm and a tread depth of 250 mm.
Step 1 — Number of risers: 2,700 mm ÷ 180 mm = 15 risers.
Step 2 — Actual riser height: 2,700 ÷ 15 = 180 mm exactly.
Step 3 — Number of treads: 15 − 1 = 14 treads.
Step 4 — Total run: 14 × 250 = 3,500 mm (3.5 m).
Step 5 — Stringer length: √(2.7² + 3.5²) = √(7.29 + 12.25) = √19.54 ≈ 4.42 m.