Stair geometry limits under IBC (US Commercial), with the governing clause for each and a worked 9-foot example. Then run your own numbers in the calculator.
The IBC governs commercial and multi-family stairs in the US — means-of-egress stairways in buildings other than one- and two-family dwellings. Its limits are tighter than the residential IRC because the stairs must safely move larger numbers of people, including under emergency egress.
| Requirement | Limit | Clause |
|---|---|---|
| Max riser height | 7.0″ | 1011.5.2 |
| Min tread depth | 11.0″ | 1011.5.2 |
| Min stair width | 44.0″ | 1011.2 |
| Min headroom | 80.0″ | 1011.3 |
| Max rise between landings | 144.0″ | 1011.6 |
For a 108-inch total rise under IBC (US Commercial): dividing by the 7.0-inch maximum riser gives a minimum of 16 risers. Spreading 108 inches evenly across 16 risers yields 6.75 inches per riser — within the limit and uniform, as the code requires.
Run your stair against IBC (US Commercial)
The IBC tightens the two dimensions that matter most for crowd movement: the maximum riser drops to 7.0 inches (from the IRC's 7.75) and the minimum tread rises to 11.0 inches (from 10.0). A stair sized to the residential limit will therefore fail an IBC plan review on both counts — the riser is too tall and the tread too shallow.
Because the envelope is narrower, the comfortable 7×11 pairing that just meets the IRC is the natural target under the IBC. If you are converting a residential design for commercial use, expect to add risers (reducing each riser's height) and deepen treads, which lengthens the total run and changes the footprint.
Compare with IRC 2018, IRC 2021, IRC 2024, UK Approved Document K, Australia NCC / BCA, Eurocode / EN.