The ceiling height is not the whole climb: the stair also has to get through the floor above. With 8 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 106" (8' 10"). That takes 14 risers of 7 9/16": 106 ÷ 7.75 = 13.68, rounded up so no riser is over the 7 3/4" limit in IRC R311.7.5.1.
With 14 risers you build 13 treads; at 10" each, the IRC R311.7.5.2 minimum, the stair runs 10' 10" across the floor. If you counted only the 96" of wall you would get 13 risers, and spread over the real 106" each one would be 8 1/8": over the limit.
The usual comfort check, 2 × riser + tread, comes to 25.1" with 10" treads, a little over the 24" to 25" range, as happens close to the 7 3/4" limit. One more riser (15 of 7 1/16", 14 treads, 11' 8" of run) brings it to 24.1".
Total rise by floor depth (8 ft ceiling)
Total rise by floor depth (8 ft ceiling)| Floor depth | Total rise | Risers | Riser height | Total run |
|---|
8"
2×8 | 104"
8' 8" | 14 | 7 7/16" | 10' 10" |
|---|
10"
2×10 | 106"
8' 10" | 14 | 7 9/16" | 10' 10" |
|---|
12"
2×12 | 108"
9' 0" | 14 | 7 11/16" | 10' 10" |
|---|
12 5/8"
11 7/8" | 108 5/8"
9' 5/8" | 15 | 7 1/4" | 11' 8" |
|---|
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 14 risers of 7 9/16", 10" treads and a 10" floor, the opening needs to be about 9' 10 7/8" 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 12.54" long on the slope: √(7.571² + 10²). Times 13 treads, each stringer measures 13' 7 1/16" along its top edge, so with about a foot extra for the plumb and level cuts it comes out of a 16 ft board. The stair climbs at 37.1°. Cut stringers are usually 2×12s; the stair calculator lays out every mark for the framing square.
Riser options for 106" of total rise
Riser options for 106" of total rise| Risers | Riser height | Treads | Total run | 2R + T |
|---|
| 14 | 7 9/16" | 13 | 10' 10" | 25.1 |
|---|
| 15 | 7 1/16" | 14 | 11' 8" | 24.1 |
|---|
| 16 | 6 5/8" | 15 | 12' 6" | 23.3 |
|---|
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 8 ft ceilings need?
14 risers and 13 treads with a 10" floor (total rise 106"). A 2×8 floor makes it 104": 14 risers of 7 7/16". 2×12 joists make it 108": 14 risers of 7 11/16".
How much floor space does a stair for 8 ft ceilings take?
10' 10" of run with 10" treads or 11' 11" 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 8 ft ceilings?
7 9/16" with a 10" floor: 106" ÷ 14 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.