The numbers come from the Construction Calculator app
What does the code allow for stairs?
| What | Limit |
|---|---|
| Riser height | 7-3/4" max |
| Tread depth | 10" min |
| Even steps | risers within 3/8" of each other, and treads too |
| Nosing | 3/4" to 1-1/4" (none needed on treads 11" or deeper) |
| Headroom | 6' 8" min |
| Width | 36" min |
| One flight | 12' 7" of rise max |
| Handrail | 34" to 38" high, on flights of 4 or more risers |
From the 2021 IRC, R311.7. Local codes differ (New York allows 8-1/4" risers and 9" treads), so check yours.
How do I work out stair steps?
- Measure the total rise, finished floor to finished floor.
- Divide by the maximum riser and round up: that is your number of risers.
- Divide the rise by the risers for the riser height.
- Treads are one fewer than risers.
- Total run = treads × tread depth.
A 106-1/2" rise at 7-3/4" risers: 106.5 ÷ 7.75 = 13.7, so 14 risers of about 7-5/8", 13 treads and 10' 10" of run. The stringer is about 14' 7-7/8" long and climbs at 37.3°.
Is an 8 inch stair riser too high?
Yes, for a home: the limit is 7-3/4". A 48" rise with 8" risers would be 6 risers; at 7-3/4" it needs 7 risers of about 6-7/8".
What is the 7-11 rule for stairs?
Risers up to 7" and treads at least 11" deep: the code limit for most stairs outside homes. The second table uses it.
What’s the code for deck stairs?
The American Wood Council’s deck guide uses the same 7-3/4" risers and 10" treads. Stairs are at least 36" wide, with a landing partway up past 12' of rise.
