Stair safety codes share a goal — a predictable, climbable, fall-resistant stair — but they reach it differently. The biggest structural difference is how they limit the length of a flight.
The US IRC allows a maximum riser of 7.75 inches with a minimum tread of 10.0 inches. The commercial IBC is stricter at 7.0 inches and 11.0 inches. The UK's Part K permits a steeper 220 mm (8.66 inch) riser for private stairs. Australia's NCC caps risers at 190 mm (7.48 inches) with a 240 mm (9.45 inch) going.
This is where they diverge most. The US codes limit a flight by maximum vertical rise between landings (147.0 inches under the IRC). The UK and Australia instead limit by the number of risers in a flight — 36 for the UK, 18 for Australia — regardless of the rise height. A calculator built only for one model will mislead users in the other jurisdictions.
Headroom clusters around 2 metres (78.7 inches) internationally, with the IRC slightly higher at 80.0 inches. Minimum width varies: 36 inches (IRC), 44 inches (IBC), 900 mm in Australia, and no fixed minimum in UK Part K.
There is no single European stair-dimension table. Eurocode covers structural loading; the geometry rules live in each member state's national regulations. Treat any single "Eurocode stair limit" with caution.
Compare the full limits on the codes hub, each with clause citations.
Take a 7.5-inch riser with a 10-inch tread. Under the US IRC it passes (riser under 7.75, tread at the 10-inch minimum). Under the stricter US IBC commercial standard it fails twice — the riser exceeds 7.0 and the tread is below 11.0. Under the UK's Part K it passes for a private stair (riser under 220 mm). The lesson: a stair is never simply "to code" — it is to code for a specific code under a specific occupancy.
The deepest divergence is how each code breaks up a tall stair. The US measures the vertical rise between landings (147 inches under the IRC). The UK and Australia count risers per flight instead — 36 and 18 respectively. For a tall flight this produces different landing positions: a US designer adds a landing when the rise crosses 147 inches; a UK designer adds one at the 36th riser regardless of how tall those risers are.
Even within one country the edition your local authority enforces decides the numbers. The IRC's stair geometry has held steady across the 2018, 2021, and 2024 editions, but the 2024 edition renumbered the stairway section (from R311.7 to R318.7), so a clause citation that was correct last year may point to the wrong number now. Always confirm both the code and the edition adopted in your jurisdiction before relying on a figure.
Unlike the IRC or Part K, the Eurocode framework sets no single prescriptive stair-dimension table. Individual member states define their own stair geometry through national rules, so "Eurocode" figures vary country to country. Treat any single Eurocode number as an estimate and verify against the relevant national annex.
Stair Headroom Rules and How to Measure · Stair Landing Requirements · The Blondel Comfort Rule for Stairs