The short answer
A US residential stair can have a riser up to 7.75 in (196 mm) and needs a tread at least 10 in (254 mm) deep. Commercial stairs are tighter: 7 in (178 mm) maximum riser and 11 in (279 mm) minimum tread. Both require 6 ft 8 in (2.03 m) of headroom.
In practice most US house stairs are built at roughly 7.25 in rise and 10.5 in run, giving a pitch near 35 degrees. European stairs are shallower and deeper on average: 170 to 200 mm rise on a 230 to 290 mm going, which produces a gentler and longer flight for the same floor-to-floor height.
US residential code: the IRC numbers
Section R311.7 of the International Residential Code governs stairs in single-family homes. The numbers that actually get checked at inspection:
| Requirement | IRC limit | Metric |
|---|---|---|
| Maximum riser height | 7.75 in | 196 mm |
| Minimum tread depth | 10 in | 254 mm |
| Minimum stair width | 36 in | 914 mm |
| Minimum headroom | 6 ft 8 in | 2.03 m |
| Handrail height | 34 to 38 in | 864 to 965 mm |
| Maximum riser variation in a flight | 3/8 in | 9.5 mm |
| Maximum tread variation in a flight | 3/8 in | 9.5 mm |
| Nosing projection (when tread under 11 in) | 0.75 to 1.25 in | 19 to 32 mm |
| Maximum vertical rise without a landing | 12 ft | 3.66 m |
The 3/8 in uniformity tolerance causes more failed inspections than any other line in the list. The human gait locks onto a stair rhythm after two or three steps, so a single riser that is half an inch off is a genuine trip hazard. The classic failure mode is the bottom step: a carpenter lays out perfect risers from the subfloor, then a 3/4 in hardwood or tile floor goes down at the bottom of the flight and shortens that one riser.
The 36 in minimum width is measured above the handrail height. Below the handrails the clear width can narrow to 31.5 in with one rail or 27 in with two.
US commercial code: the IBC numbers
Section 1011 of the International Building Code applies to means-of-egress stairs in commercial and multi-family buildings, and it is noticeably stricter.
| Requirement | IBC limit | Metric |
|---|---|---|
| Maximum riser height | 7 in | 178 mm |
| Minimum riser height | 4 in | 102 mm |
| Minimum tread depth | 11 in | 279 mm |
| Minimum width (occupant load under 50) | 36 in | 914 mm |
| Minimum width (occupant load 50+) | 44 in | 1,118 mm |
| Minimum headroom | 80 in | 2.03 m |
| Maximum vertical rise between landings | 12 ft | 3.66 m |
The 7-and-11 combination is the reference geometry for most public buildings in the US. It gives a pitch of 32.5 degrees, shallow enough that a crowd can descend it quickly under evacuation conditions without the cascade risk of a steeper flight.
Note the minimum riser height of 4 in on the commercial side. There is no minimum in residential code, but a single very shallow step in a walkway is a well-documented hazard because people do not perceive it as a step at all.
The Blondel rule and European geometry
European stair design descends from a formula published by the French architect François Blondel in 1675. The rule states that two risers plus one going should equal the length of an average human pace:
The reasoning is that a person climbing a stair uses the same total stride energy as a person walking on the flat, so as the risers get taller the treads must get shorter to keep the stride consistent. It works remarkably well and remains embedded in national standards.
| Country / standard | Max rise | Min going | Max pitch |
|---|---|---|---|
| UK (Approved Document K, private stair) | 220 mm (8.66 in) | 220 mm (8.66 in) | 42 degrees |
| Germany (DIN 18065, required stair) | 190 mm (7.48 in) | 260 mm (10.24 in) | roughly 37 degrees |
| France (NF P01-012, dwelling) | 170 to 180 mm typical | 280 mm typical | 30 to 35 degrees |
| US residential (IRC) | 196 mm (7.75 in) | 254 mm (10 in) | roughly 38 degrees |
| US commercial (IBC) | 178 mm (7 in) | 279 mm (11 in) | 32.5 degrees |
The UK allows the steepest private stair in this group. A 220 mm rise on a 220 mm going is a 45-degree geometry on paper, held to 42 degrees by the requirement that 2R + G stay within 550 to 700 mm. Anyone who has climbed a Victorian terrace staircase in London and then a suburban US stair has felt this difference directly.
The US number to watch when reading European drawings is the going versus the tread. “Going” is the horizontal distance from one nosing to the next. “Tread depth” in US code is measured the same way, nosing to nosing, not the physical width of the timber. Confusing the two adds an inch of phantom depth per step. The metric blueprint conversion guide covers the other terminology traps in the same family.
Laying out a real flight
Stair layout is arithmetic on the floor-to-floor height, not the ceiling height. Floor-to-floor is the ceiling height plus the floor assembly, which in typical US framing adds 10 to 14 in for joists, subfloor, and finish floor.
Worked example for a common US house:
- Ceiling height 8 ft (2.44 m), floor assembly 12 in, so floor-to-floor is 108 in (2.74 m).
- Divide by a target riser of 7.25 in: 108 / 7.25 = 14.9, so use 15 risers.
- Actual riser: 108 / 15 = 7.2 in (183 mm), comfortably under the 7.75 in cap.
- A flight always has one fewer tread than risers, so 14 treads.
- At a 10.5 in run, total horizontal length is 14 × 10.5 = 147 in (12 ft 3 in, or 3.73 m).
- Check Blondel: (2 × 7.2) + 10.5 = 24.9 in (632 mm). Inside the band.
The same exercise with a 9 ft ceiling pushes floor-to-floor to about 120 in (3 m) and calls for 16 or 17 risers, adding roughly a foot of floor length. This is the hidden cost of the move to taller ceilings that we cover in standard ceiling heights for US homes: a 9 ft first floor does not just raise the walls, it eats another 10 to 12 in of floor plan for the staircase.
Headroom is checked along the pitch line, measured vertically from the nosing of each tread. The tightest point is almost always where the flight passes under the upper floor opening. If a plan shows the stairwell opening ending too early, the fix is to lengthen the opening, not to shorten the stair.
Handrails, landings, and spiral stairs
Handrails must be 34 to 38 in (864 to 965 mm) above the nosing line, with a graspable profile: 1.25 to 2 in (32 to 51 mm) diameter for a round rail, or an equivalent perimeter for a shaped one. Guards along an open side must be 36 in (914 mm) minimum in residential and 42 in (1.07 m) in commercial, with the 4-inch sphere rule for baluster spacing.
Landings must be at least as deep as the stair is wide, with 36 in the practical floor. Any flight with more than 12 ft (3.66 m is the nearest reference value) of vertical rise needs an intermediate landing, which in a house with 3 m floor-to-floor heights means the stair between two floors is fine but a straight run through two floors is not.
Spiral stairs get their own relaxed rules under IRC R311.7.10.1: a minimum clear width of 26 in (660 mm), a minimum tread depth of 6.75 in (171 mm) measured 12 in from the narrow edge, a maximum riser of 9.5 in (241 mm), and 6 ft 6 in (1.98 m) of headroom rather than 6 ft 8 in. They are legal as a secondary stair almost everywhere and legal as the sole means of egress from a habitable space in far fewer jurisdictions than homeowners assume.
For any dimension not in these tables, the meters-to-feet calculator converts arbitrary values. The ones worth memorizing are the headroom minimum of 2.03 m, the 3.66 m landing rule, and the fact that a standard flight consumes roughly 3.5 to 3.8 m of floor length per story. That last figure is the number that decides whether a staircase fits in a floor plan at all, and it is worth checking before anything else.
Sources and further reading:
- ICC: 2024 International Building Code, Section 1011.5.2 (riser height and tread depth)
- ICC: International Residential Code, Section R311.7 (stairways)
- Lapeyre Stair: Maximum stair riser height and minimum tread depth code
- Family Handyman: Standard stair rise and run
- Our guide: Standard ceiling heights for US homes