Commercial Stair Dimensions: Width, Treads, Risers & OSHA Rules

There is no single U.S. dimension that applies to every commercial stair. For a building egress stair, the locally adopted building code controls; OSHA’s workplace stair rule addresses a different use case. The figures below use the 2021 International Building Code (IBC) as a model-code example and federal OSHA general-industry requirements for workplace stairs. Always confirm the edition and amendments adopted by the authority having jurisdiction.

These are not competing measurements: IBC egress sizing and OSHA workplace stairs apply in different contexts. See the 2021 IBC stair-width rule, IBC tread and riser dimensions, and OSHA 29 CFR 1910.25.

For ordinary means-of-egress stairs, the 2021 IBC sets a 44-inch minimum, with a 36-inch exception for stairs serving fewer than 50 occupants. Required width can also increase with occupant load. Accessible means-of-egress stairs have a separate 48-inch clear-width provision between handrails, subject to code exceptions such as qualifying sprinkler protection. Check the building’s occupancy, egress arrangement and adopted code before using a number.

OSHA’s 22-inch minimum applies to standard stairs in covered general-industry workplaces, measured between vertical barriers. That is not a general substitute for a building-code egress stair width. Use the rule that applies to the actual space and approval path. See IBC Section 1011.2, IBC accessible stairway width, and OSHA Section 1910.25(c)(4).

Under the 2021 IBC example, a typical rectangular egress-stair tread is at least 11 inches deep and each riser is 4 to 7 inches high. The risers and treads in one flight must stay consistent within the tolerances in the adopted code. The stair headroom minimum is 80 inches, measured vertically from a line connecting the tread nosings. These dimensions describe a building-code stair, not a universal “average stair.”

For OSHA standard stairs in general-industry workplaces, the federal rule instead sets a maximum riser height of 9.5 inches and minimum tread depth of 9.5 inches; vertical clearance is at least 6 feet 8 inches. Because the standards differ, identify whether a project is an egress stair, a workplace access stair, or both, then apply the stricter applicable requirements. Sources: IBC Section 1011.5.2, IBC headroom provision, and OSHA stair requirements.

A stair’s horizontal run is calculated from its number of treads and the chosen tread depth; there is no reliable single average stair length. First measure the finished-floor-to-finished-floor rise. Divide that rise into equal risers that comply with the applicable maximum, then determine the tread count and total run. For example, 12 risers at 7 inches produce an 84-inch rise; the actual run depends on the permitted tread depth and layout.

The stair opening must preserve the required headroom over the full path of travel. Its size therefore depends on floor thickness, stair pitch, landing arrangement and direction of travel—not just stair width. Before construction, confirm the code edition, occupant load, clear width between handrails, landing geometry, handrails/guards, headroom, door swings, accessible-egress provisions and structural support with the local building official or licensed designer. For a home staircase, see our residential stair dimensions guide.