What is the standard stair riser height and tread depth?
The 2021 IRC caps a riser at 7 3/4" and a tread at no less than 10". Comfortable is nearer 7" and 11". Every dimension the code sets, and which of them people get wrong.
The IRC maximum riser is 7 3/4" and the minimum tread depth is 10".
Those are limits, not targets. A comfortable stair lands around 7" of riser and 11" of tread — inside the limits with room to spare, which is where you want to be when the inspector's tape disagrees with yours by a sixteenth.
How that is worked out
- Riser height is measured vertically from the top of one tread to the top of the next. Tread depth is measured nosing to nosing, horizontally — not the depth of the tread board, which is larger by the nosing overhang.
- The limits are a maximum on the riser (7 3/4") and a minimum on the tread (10"). Both have to hold at once.
- The consistency rule bites hardest: no more than 3/8" between the tallest and shortest riser in a flight, and the same for treads.
2021 IRC stair dimensions
| Dimension | Requirement | Why it is there |
|---|---|---|
| Maximum riser height | 7 3/4" | Above this the stair is tiring to climb and awkward to descend. |
| Minimum tread depth | 10" | Nosing to nosing. Less and the ball of your foot overhangs on the way down. |
| Maximum riser variation | 3/8" | Across the whole flight. An inconsistent riser is what people actually fall on. |
| Minimum stair width | 36" | Clear width above the handrail. |
| Minimum headroom | 80" | Measured plumb from the nosing line. Set by the floor opening above. |
| Nosing projection | 3/4" – 1 1/4" | Required where the tread is under 11" deep. |
| Maximum rise between landings | 12 ft 7 in | A flight taller than this needs a landing in it. |
| Handrail height | 34" – 38" | Measured from the tread nosing line. Not the same number as a guard's height. |
Worth knowing
- These are 2021 IRC figures and they are defaults, not law. Jurisdictions amend them, commercial work follows a different code entirely, and the building department decides. Ring them before you cut stringers.
- The riser variation rule is the one that fails inspections. It is usually the bottom step, where the stringer has to be cut down by the thickness of the tread stock — forget that and the bottom riser is a full tread thicker than the rest.
- Measure finished floor to finished floor. A stair laid out before the flooring goes down, and not adjusted for it, ends up with one riser out by the thickness of the finish.
- The tread depth in the code is the unit run, nosing to nosing. The tread board itself is deeper than that by the nosing overhang, which is what you cut it to.
Work out your own numbers
- Stair stringers
Divide the rise into even risers, lay out the notches, and check the result against the code.
Related questions
- What is the maximum riser height for stairs?
- 7 3/4" under the 2021 IRC for a residential stair, measured vertically from one tread surface to the next. Commercial work under the IBC is tighter at 7". Your local amendments can be tighter still, which is why this is a starting point and not an answer to build on.
- Can all my risers be slightly different?
- No, and this is the rule that fails more inspections than any other. The tallest and the shortest riser in a flight can differ by no more than 3/8". Consistency matters more than the absolute height — people climb stairs on autopilot, and a step that is not where the last one implied is where they trip.
- What is the ideal rise and run for stairs?
- About a 7" riser with an 11" tread. Two old rules of thumb both land near there: riser plus tread between 17" and 18", and twice the riser plus the tread around 25". Both sit comfortably inside the IRC limits, which is where a stair should be rather than scraping the maximum.