Home & Construction⏱ 5 min read
How to Calculate Staircase Rise and Run: The Builder's Formula
Building or renovating stairs requires precise calculation — get the rise-to-run ratio wrong and stairs are uncomfortable or dangerous. Here's the complete formula with UK building regulations.
Staircases look simple but the geometry is exacting. The relationship between rise (vertical height of each step) and run (horizontal depth) determines comfort, safety, and compliance with building regulations.
The Key Measurements
Total Rise = Floor-to-floor height (including floor thickness)
Number of risers = Number of steps
Individual Rise = Total Rise ÷ Number of risers
Going (Run) = Horizontal distance of each tread
Total Going = Individual Run × (Number of risers − 1)
(Last riser lands on upper floor, so one fewer tread)
UK Building Regulations (Part K)
MeasurementPrivate StairCommon/Commercial
Maximum rise220mm180mm
Minimum going220mm250mm
Minimum width800mm1,000mm+
Minimum headroom2,000mm2,000mm
The Comfort Formula
Building regulations set the limits; the comfort formula sets the ideal. The traditional rule, used by builders for centuries:
2 × Rise + Going = 550mm to 700mm (comfort zone)
Ideal: 2R + G = 630mm
Examples:
Rise 175mm, Going 280mm: 2(175) + 280 = 630 ✓ (ideal)
Rise 200mm, Going 250mm: 2(200) + 250 = 650 ✓ (acceptable)
Rise 220mm, Going 220mm: 2(220) + 220 = 660 ✓ (steep but legal)
Worked Example: Standard House
Floor-to-floor height: 2,700mm
Target rise: ~175mm (comfortable)
Number of risers = 2,700 ÷ 175 = 15.4 → round to 15 or 16
With 15 risers:
Individual rise = 2,700 ÷ 15 = 180mm ✓ (within regulations)
Comfort: 2(180) + G = 630 → G = 270mm ✓
Total going = 270mm × 14 = 3,780mm
(14 treads because 15 risers = 14 treads + landing)
Calculating Stringer Length
Stringer = √(Total Rise² + Total Going²)
Example above:
= √(2,700² + 3,780²)
= √(7,290,000 + 14,288,400)
= √21,578,400
= 4,645mm ≈ 4.6m
Common Mistakes to Avoid
- Inconsistent rise: All risers must be within 5mm of each other — the most common tripping hazard on self-built stairs
- Forgetting floor thickness: Total rise includes the finished floor on both levels; use finished floor-to-finished floor height
- Headroom check: Measure headroom at the most restrictive point — often 1,500mm along the stringer from where the stair meets the upper floor
- Nosing: Treads typically have a 25mm nosing (overhang) — this adds to the effective going without adding to the pitch line going