The short answer
For home stairs in the US, the International Residential Code (IRC) allows risers up to 7¾ in and requires treads at least 10 in deep. Many builders aim for something gentler, around 7 to 7½ in risers with 10 to 11 in treads. Canada, Australia and many US cities set their own figures, so always check local code.
Rise and run terms
- Riser height (unit rise): the vertical distance from one tread surface to the next.
- Tread depth (unit run): the horizontal distance from the front edge of one tread to the front edge of the next, measured nose to nose.
- Total rise: finished floor to finished floor.
- Total run: the horizontal length of the whole flight.
- Nosing: the part of the tread that sticks out past the riser below.
Common limits
| Item | US homes (IRC) | US commercial (IBC) |
|---|---|---|
| Riser height | 7¾ in maximum | 4 to 7 in |
| Tread depth | 10 in minimum | 11 in minimum |
| Variation in a flight | ⅜ in maximum | ⅜ in maximum |
| Headroom | 6 ft 8 in | 80 in |
Codes change and are adopted with local amendments. Treat this as a guide to what to ask your building department, not as the final word.
Comfort rules of thumb
Within the code limits, these old rules help pick a pair that feels right. They describe a normal walking stride.
| Rule | Target | 7.2 in riser, 10 in tread | 7.5 in riser, 10 in tread |
|---|---|---|---|
| 2 × riser + tread | 24 to 25 in | 24.4 in | 25 in |
| riser + tread | 17 to 18 in | 17.2 in | 17.5 in |
| riser × tread | 70 to 75 | 72 | 75 |
A stair built right at the IRC maximum, 7¾ in risers on 10 in treads, scores 25.5 in on the first rule: legal, but on the steep side. A deeper tread helps.
How many steps for common floor heights
The table assumes you aim for risers of 7½ in or less and 10 in treads. Total rise includes the floor framing and finishes, so measure yours rather than relying on ceiling height.
| Total rise | Risers | Riser height | Treads | Total run |
|---|---|---|---|---|
| 96 in | 13 | 7.38 in | 12 | 10 ft |
| 102 in | 14 | 7.29 in | 13 | 10 ft 10 in |
| 108 in | 15 | 7.2 in | 14 | 11 ft 8 in |
| 114 in | 16 | 7.13 in | 15 | 12 ft 6 in |
| 120 in | 16 | 7.5 in | 15 | 12 ft 6 in |
Worked example
A stair to a split-level family room has a total rise of 100 in, and you want roomy 10½ in treads. Dividing by a 7½ in target gives 13.3, so you need 14 risers of about 7.14 in, just over 7⅛ in. There are 13 treads, and the stair runs 11 ft 4½ in across the floor. The comfort check works out at 2 × 7.14 + 10.5 = 24.8 in, inside the 24 to 25 in target. If the room cannot spare that much floor, you could allow risers up to 7¾ in: 13 risers of about 7.69 in, 12 treads and a 10 ft 6 in run. That saves 10½ in of floor, but the comfort figure rises to 25.9 in and the stair feels steeper. Try both in the stair calculator.
Short stairs and deck steps
The same rules apply to two or three steps at a door or deck. A 30 in deck height with a 7½ in target gives 4 risers of exactly 7½ in and 3 treads. Uneven steps on short flights are a common trip hazard, so measure the landing spot carefully: soil, pavers or a concrete pad all change the total rise.
Landings and long flights
The IRC limits a single flight to 151 in (12 ft 7 in) of vertical rise between floors or landings. Landings are also needed at the top and bottom of each stair, at least as wide as the stair and at least 36 in deep in the direction of travel. A landing partway up also lets you turn the stair 90 or 180 degrees, which can solve a space problem when a straight run is too long.
Practical tips
- Every riser in a flight must match within ⅜ in, including the first and last. Account for finished flooring at the top and bottom before you cut stringers.
- When treads are less than 11 in deep, the IRC requires a nosing of ¾ to 1¼ in on stairs with solid risers.
- Handrails are required on stairs with four or more risers under the IRC. Plan for them early, because they affect the clear width.
- Stairs are structural and a fall hazard. Get a permit where required and have the work inspected.
Frequently asked questions
What is the standard rise and run for stairs?
Under the US IRC, risers may be up to 7¾ in and treads must be at least 10 in deep. A comfortable home stair is often about 7 to 7½ in rise with 10 to 11 in run.
How many stairs for a 9 ft ceiling?
It depends on the total rise, which includes the floor framing. A 108 in rise needs 15 risers at 7.2 in; a 120 in rise needs 16 risers at 7.5 in.
What is the 2R + T rule?
Two riser heights plus one tread depth should total about 24 to 25 in. A 7.2 in riser with a 10 in tread gives 24.4 in.
Do the math for your own project.
Open the stair calculator