Quick answer
Under the 2021 International Residential Code, a riser can be at most 7-3/4 inches tall and a tread at least 10 inches deep, and no riser or tread in a flight may differ from the others by more than 3/8 inch. Stairs must be at least 36 inches wide with 6 ft 8 in of headroom, and any flight with four or more risers needs a handrail 34 to 38 inches high.
Risers and treads
- Riser height: no more than 7-3/4 inches, measured between the leading edges of the treads (R311.7.5.1).
- Tread depth: at least 10 inches, measured between the front edges of the nosings (R311.7.5.2).
- Consistency: the tallest riser in a flight may exceed the shortest by no more than 3/8 inch, and the same goes for tread depth. That is why the top and bottom steps need the same rise as the rest, including the finished floor or decking.
- Nosings: a nosing projection of 3/4 to 1-1/4 inches is required, unless the treads are at least 11 inches deep (R311.7.5.3).
- Open risers: where openings are more than 30 inches above the floor or grade below, they must not let a 4-inch sphere pass (R311.7.5.1).
How many steps you need
Measure the total rise, from the landing or ground surface to the top of the finished deck or floor. Divide by 7.75 and round up: that is the number of risers. Divide the total rise by that number for the actual riser height, so every step comes out equal. When the deck or floor is the top step, there is one fewer tread than risers.
| Total rise | Risers | Each riser | Treads (deck as top step) | Run at 10 in treads |
|---|---|---|---|---|
| 24 in | 4 | 6 in | 3 | 30 in |
| 30 in | 4 | 7.5 in | 3 | 30 in |
| 36 in | 5 | 7.2 in | 4 | 40 in |
| 48 in | 7 | 6.86 in | 6 | 60 in |
| 60 in | 8 | 7.5 in | 7 | 70 in |
| 96 in | 13 | 7.38 in | 12 | 120 in |
| 108 in | 14 | 7.71 in | 13 | 130 in |
The stair stringer calculator does this for your measured rise (it aims for a more comfortable 7-1/2 inch riser unless you change the target) and lays out the stringer cuts.
Width, headroom and landings
- Width: at least 36 inches clear above handrail height; at and below the handrail, at least 31-1/2 inches with one handrail or 27 inches with two (R311.7.1).
- Headroom: at least 6 ft 8 in, measured from the sloped line of the nosings (R311.7.2).
- Height of one flight: no more than 12 ft 7 in between floors or landings (R311.7.3). The American Wood Council's DCA 6 deck guide is stricter for deck stairs and calls for a landing above 12 ft of rise.
- Landings: a floor or landing at the top and bottom of each stairway, at least as wide as the stair and at least 36 inches deep on a straight run (R311.7.6).
Handrails
- Required on at least one side of any flight with four or more risers (R311.7.8).
- Height 34 to 38 inches, measured from the sloped line of the nosings (R311.7.8.1).
- Continuous from above the top riser to above the lowest riser, with ends returned to a wall or post (R311.7.8.4).
- Graspable: a round rail 1-1/4 to 2 inches in diameter, or a shape of equivalent grip (R311.7.8.5).
- The open side of a stair more than 30 inches above grade also needs a guard at least 34 inches high; see deck railing rules.
Deck stairs
DCA 6 adds details for wood deck stairs: 2x12 stringers at least, cut stringers spanning no more than 6 ft and spaced no more than 18 inches apart, at least three cut stringers on a 36-inch stair, and stair guards with posts no more than 6 ft apart.
The 2024 code and local rules
The 2024 IRC keeps the same numbers but moves the stair rules to section R318.7 and handrails to R320, and adds some landing exceptions for short exterior stairs. Some states amend the stair rules; New Jersey, for example, allows 8-1/4 inch risers and 9 inch treads. Your building department has the final word.
Frequently asked questions
What is the maximum stair riser height?
7-3/4 inches under the 2021 IRC (R311.7.5.1), with no more than 3/8 inch difference between the tallest and shortest riser in a flight.
What is the minimum stair tread depth?
10 inches, measured between the nosings (2021 IRC R311.7.5.2). Treads under 11 inches need a 3/4 to 1-1/4 inch nosing.
How many steps for a 30 inch rise?
4 risers of about 7.5 inches each, with 3 treads if the deck is the top step.
When do stairs need a handrail?
When a flight has four or more risers, on at least one side, 34 to 38 inches above the nosings (2021 IRC R311.7.8).
Calculators for this
Stair Stringer
Enter the total rise to get riser height, step count, stringer length and a to-scale layout diagram with IRC code checks.
Deck Railing and Baluster
Find how many balusters and posts your deck railing needs.
Deck Framing Planner
Joist and beam size, post spacing, post and footing size and ledger fasteners, with a to-scale framing plan.
Published 2026-11-06. Sources: 2021 International Residential Code, section R311.7 (Colorado adoption, via UpCodes); 2024 International Residential Code, chapter 3 (Maryland adoption, via UpCodes); 2024 International Residential Code as amended by New Jersey (via UpCodes); American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide. See how we calculate.