The ceiling height is not the whole climb: the stair also has to get through the floor above. With 9 ft from floor to ceiling and a common 10" floor (2×10 joists at 9 1/4" plus a 3/4" subfloor), the total rise is 118" (9' 10"). That takes 16 risers of 7 3/8": 118 ÷ 7.75 = 15.23, rounded up so no riser is over the 7 3/4" limit in IRC R311.7.5.1.
With 16 risers you build 15 treads; at 10" each, the IRC R311.7.5.2 minimum, the stair runs 12' 6" across the floor. If you counted only the 108" of wall you would get 14 risers, and spread over the real 118" each one would be 8 7/16": over the limit.
The usual comfort check, 2 × riser + tread, comes to 24.8" with 10" treads, inside the 24" to 25" range that feels natural. One more riser (17 of 6 15/16", 16 treads) makes each step lower and stretches the run to 13' 4".
Total rise by floor depth (9 ft ceiling)
Total rise by floor depth (9 ft ceiling)| Floor depth | Total rise | Risers | Riser height | Total run |
|---|
8"
2×8 | 116"
9' 8" | 15 | 7 3/4" | 11' 8" |
|---|
10"
2×10 | 118"
9' 10" | 16 | 7 3/8" | 12' 6" |
|---|
12"
2×12 | 120"
10' 0" | 16 | 7 1/2" | 12' 6" |
|---|
12 5/8"
11 7/8" | 120 5/8"
10' 5/8" | 16 | 7 9/16" | 12' 6" |
|---|
Stairwell opening
Headroom sets how long the hole in the upper floor has to be. IRC R311.7.2 asks for at least 6' 8" measured plumb from the line through the tread nosings. With 16 risers of 7 3/8", 10" treads and a 10" floor, the opening needs to be about 10' 2 1/16" long, measured level from the top riser back to the header. Add the thickness of any drywall or trim on the header.
Stringers and slope
One riser and one 10" tread make a step 12.43" long on the slope: √(7.375² + 10²). Times 15 treads, each stringer measures 15' 6 3/8" along its top edge, so with about a foot extra for the plumb and level cuts it comes out of a 18 ft board. The stair climbs at 36.4°. Cut stringers are usually 2×12s; the stair calculator lays out every mark for the framing square.
Riser options for 118" of total rise
Riser options for 118" of total rise| Risers | Riser height | Treads | Total run | 2R + T |
|---|
| 16 | 7 3/8" | 15 | 12' 6" | 24.8 |
|---|
| 17 | 6 15/16" | 16 | 13' 4" | 23.9 |
|---|
| 18 | 6 9/16" | 17 | 14' 2" | 23.1 |
|---|
Measuring and code notes
Measure from finished floor to finished floor. If the lower floor will get tile or the upper floor hardwood, add their thickness now; otherwise the first or last riser comes out different from the rest.
IRC R311.7.5.1 also keeps the tallest and shortest riser in a flight within 3/8" of each other, and R311.7.8 calls for a handrail on at least one side of any flight with four or more risers. Local codes can be stricter; check with your building department before you cut.
Frequently asked questions
How many steps do 9 ft ceilings need?
16 risers and 15 treads with a 10" floor (total rise 118"). A 2×8 floor makes it 116": 15 risers of 7 3/4". 2×12 joists make it 120": 16 risers of 7 1/2".
How much floor space does a stair for 9 ft ceilings take?
12' 6" of run with 10" treads or 13' 9" with 11" treads, plus a landing at least 36" deep at the bottom (IRC R311.7.6). IRC R311.7.1 sets 36" as the minimum width.
How tall is each step with 9 ft ceilings?
7 3/8" with a 10" floor: 118" ÷ 16 risers. That keeps every riser at or under the 7 3/4" maximum in IRC R311.7.5.1.
Estimates only. Check measurements, product labels and local building codes before you buy or build.