Stair Calculator — Rise, Run, Angle & Stringer Length
Calculate stair rise, run (tread depth), number of steps, stringer length and headroom clearance. Verify compliance with building code requirements — supports both IRC (US) and TEK17/NS3940 (Norway/EU) standards.
How the stair calculator works
- 1Number of risers: total rise (floor-to-floor height) ÷ target riser height, rounded to nearest whole number
- 2Actual riser height: total rise ÷ number of risers (must be consistent — never vary by more than 5 mm)
- 3Tread depth (run): use the rule 2R + T = 630 mm (R = riser, T = tread)
- 4Total run: (number of risers − 1) × tread depth
- 5Stringer length: √(total rise² + total run²)
- 6Headroom: measure vertically from each tread nosing to any obstruction above — minimum 2.0 m (UK/EU) or 6'8" (US)
Worked example
Floor-to-floor height: 2.75 m. Target riser height: 175 mm.
2750 ÷ 175 = 15.7 → round to 16 risers. Actual riser: 172 mm. Tread depth: 630 − (2×172) = 286 mm. Total run: 15 × 286 = 4.29 m. Stringer length: √(2.75² + 4.29²) = 5.11 m.
Frequently asked questions
What is the standard rise and run for stairs?
IRC (US): max riser 7.75 in (197 mm), min tread 10 in (254 mm). UK Building Regs: riser 155–220 mm, going 245–260 mm for private stairs. The rule 2R + T = 630 mm is widely used as a comfort guide.
How do I calculate the number of steps for a staircase?
Divide the total floor-to-floor height by your target riser height (typically 170–180 mm). Round to the nearest whole number. Then recalculate the exact riser by dividing the total height by the step count.
What is the minimum headroom for a staircase?
UK: 2.0 m measured vertically from the pitch line. US IRC: 6 ft 8 in (2.03 m). Loft stairs can be reduced to 1.8 m in some jurisdictions. Always measure at each tread nosing.
How long should stair stringers be?
Stringer length = √(total rise² + total run²). For a standard 2.75 m rise and 4.3 m run, the stringer is about 5.1 m. Allow extra length (300 mm) for the bearing at top and bottom.
What wood is best for stair treads?
Oak, ash and beech are the most durable for exposed treads. Pine is more affordable but dents more easily. For a painted finish, structural softwood (C24) with solid hardwood nosings is a good compromise.