The drawing shows the stair from the side, to scale, with the floor above in gray. The gap in that floor is the stairwell opening, and the dashed line at its edge is the headroom you asked for.
The short answer for common ceilings
Each row adds a typical floor to the ceiling height to get the total rise, then divides it into equal risers that stay at or under the max. Two limits are shown. A 7 3/4″ max riser is common for homes in the US. A 7″ max gives a gentler stair and is a common limit for public buildings.
| Ceiling | Floor between | Total rise | Risers, 7 3/4″ max | Treads and run at 10″ | Risers, 7″ max |
|---|---|---|---|---|---|
| 8 ft | 2×8 joists | 8′ 8 1/2″ | 14 at 7 7/16″ | 13, 10′ 10″ | 15 at 6 15/16″ |
| 2×10 joists | 8′ 10 1/2″ | 14 at 7 5/8″ | 13, 10′ 10″ | 16 at 6 11/16″ | |
| 2×12 joists | 9′ 0 1/2″ | 14 at 7 3/4″ | 13, 10′ 10″ | 16 at 6 13/16″ | |
| 11 7/8″ engineered joists | 9′ 1 1/8″ | 15 at 7 1/4″ | 14, 11′ 8″ | 16 at 6 13/16″ | |
| 9 ft | 2×8 joists | 9′ 8 1/2″ | 16 at 7 5/16″ | 15, 12′ 6″ | 17 at 6 7/8″ |
| 2×10 joists | 9′ 10 1/2″ | 16 at 7 7/16″ | 15, 12′ 6″ | 17 at 7″ | |
| 2×12 joists | 10′ 0 1/2″ | 16 at 7 9/16″ | 15, 12′ 6″ | 18 at 6 11/16″ | |
| 11 7/8″ engineered joists | 10′ 1 1/8″ | 16 at 7 9/16″ | 15, 12′ 6″ | 18 at 6 3/4″ | |
| 10 ft | 2×8 joists | 10′ 8 1/2″ | 17 at 7 9/16″ | 16, 13′ 4″ | 19 at 6 3/4″ |
| 2×10 joists | 10′ 10 1/2″ | 17 at 7 11/16″ | 16, 13′ 4″ | 19 at 6 7/8″ | |
| 2×12 joists | 11′ 0 1/2″ | 18 at 7 3/8″ | 17, 14′ 2″ | 19 at 7″ | |
| 11 7/8″ engineered joists | 11′ 1 1/8″ | 18 at 7 3/8″ | 17, 14′ 2″ | 20 at 6 11/16″ |
So the same 9 foot ceiling can mean 16 steps or 18, depending on the floor and the riser limit. If you've seen different answers for one ceiling height, that's usually why. They assume a different floor or a different max riser.
Why the ceiling height isn't the total rise
A stair climbs from the finished floor below to the finished floor above. The ceiling height only gets you to the underside of the ceiling. Above it sit the drywall, the joists, the subfloor and whatever flooring goes on top, and the stair has to climb all of that too.
With 2×10 joists that's about 10 1/2″: 1/2″ of drywall, 9 1/4″ of joist and a 3/4″ subfloor. Add 3/4″ hardwood upstairs and it's 11 1/4″. Each extra inch of floor is a little over an eighth of a riser, so a thick floor is often what tips a stair into one more step.
If the floors are already in, skip all this and measure the total rise directly, from the finished floor below to the finished floor above, at the spot where the stair will be. Then type that into the stair stringer calculator for the full layout.
Steps, risers and treads
When people ask how many stairs, they usually mean how many times you step up. That's the number of risers. The number of treads is one fewer, because the last step lands you on the upper floor, and that floor acts as the top tread.
So a 16 riser stair has 15 treads. It's an easy one to get wrong when you're buying tread boards, or when a plan lists "15 steps" and means treads.
A worked example: a 9 foot ceiling
Say the ceiling is 9′ 0″, the floor above is framed with 2×10s, and you want risers no taller than 7 3/4″ with 10″ treads. These are the numbers already in the calculator.
- Find the total rise.
108″ of ceiling plus 10 1/2″ of floor is 118 1/2″, or 9′ 10 1/2″.
- Divide by the max riser and round up.
118 1/2″ divided by 7 3/4″ is 15.29. You can't have part of a step, and rounding down would make every riser taller than the max, so it's 16 risers.
- Get the exact riser height.
118 1/2″ over 16 risers is 7.406″, which marks as 7 7/16″ on a tape.
- Count the treads and the run.
15 treads of 10″ make a run of 12′ 6″. The stair climbs at 36.5°.
- Size the opening.
For 6′ 8″ of headroom, the floor above needs an opening of about 10′ 2 3/16″, measured back from the top riser. The next section shows where that number comes from.
How much floor the stair takes
The run is the floor space from the face of the bottom riser to the face of the top one. For the example it's 12′ 6″, so a 9 foot ceiling needs about 12 1/2 feet of straight floor for the stair alone.
That's before the landing. At the top you step straight onto the upper floor, but the bottom needs clear floor to step off. Many codes ask for a landing at least as deep as the stair is wide, often 36″. So plan on about 15 1/2 feet of length for a straight stair under a 9 foot ceiling. If you don't have it, an L or U stair with a landing halfway folds the same climb into less length.
A deeper tread makes the stair easier to climb but longer. With 11″ treads, the same 15 treads run 13′ 9″.
The stairwell opening and headroom
As you climb, the floor above gets closer to your head. Somewhere along the stair it would hit you, so the upper floor has to be cut open from that point to the top. Headroom is measured straight up from the line that touches the front edge of every tread, and 6′ 8″ is a common minimum.
Here's the trick for working out the opening. That line rises one riser for every tread you go forward. To get the headroom plus the floor thickness, 90 1/2″ in the example, you need that many inches of climb, and each inch of climb takes tread ÷ riser inches of length. So:
Opening length = (headroom + floor thickness) × tread ÷ riser
For the example: 90 1/2″ × 10 ÷ 7.406″ is about 10′ 2 3/16″. That's measured back from the top riser, and it's the clear opening after the framing goes in. A steeper stair needs a shorter opening, and a deeper tread needs a longer one.
Deck steps and short flights
The same rule works for any rise, from two porch steps to a split level. Measure from the ground or the lower surface to the top of the deck or floor, then divide by the max riser and round up.
| Total rise | Risers | Riser height | Treads | Run |
|---|---|---|---|---|
| 1′ 6″ | 3 | 6″ | 2 | 1′ 8″ |
| 2′ 0″ | 4 | 6″ | 3 | 2′ 6″ |
| 2′ 6″ | 4 | 7 1/2″ | 3 | 2′ 6″ |
| 3′ 0″ | 5 | 7 3/16″ | 4 | 3′ 4″ |
| 3′ 6″ | 6 | 7″ | 5 | 4′ 2″ |
| 4′ 0″ | 7 | 6 7/8″ | 6 | 5′ 0″ |
| 4′ 6″ | 7 | 7 11/16″ | 6 | 5′ 0″ |
| 5′ 0″ | 8 | 7 1/2″ | 7 | 5′ 10″ |
| 6′ 0″ | 10 | 7 3/16″ | 9 | 7′ 6″ |
| 7′ 0″ | 11 | 7 5/8″ | 10 | 8′ 4″ |
For a deck, measure where the bottom step will land, not at the house. Yards slope, and an inch of fall over the run changes the riser height.
What this calculator doesn't check
It does the geometry, nothing more. The 7 3/4″ riser, 10″ tread and 6′ 8″ headroom are common limits in US homes, but codes vary from place to place, and the numbers you type are yours, not a code. It doesn't size the joists around the opening, check handrails or think about a landing. Check your local code before you frame anything.
Questions
How many stairs for an 8 foot ceiling?
Usually 14. An 8 foot ceiling with 2×10 joists gives a total rise of 8′ 10 1/2″, which takes 14 risers of 7 5/8″ at a 7 3/4″ max. Engineered joists or a 7″ max riser push it to 15 or 16.
How many stairs for a 9 foot ceiling?
Usually 16. With 2×10 joists the total rise is 9′ 10 1/2″, and 16 risers of 7 7/16″ cover it. At a 7″ max it takes 17 or 18.
How many stairs for a 10 foot ceiling?
17 or 18. With 2×10 joists the total rise is 10′ 10 1/2″, which takes 17 risers of 7 11/16″. With 2×12s or engineered joists it's 18.
How many steps are in a normal flight of stairs?
Between floors in a house, usually 14 to 17 risers, depending on the ceiling height and the floor. Many codes also limit how much one flight can climb before it needs a landing, often about 12 1/2 feet.
Does the top floor count as a step?
It counts as the last tread, not as a riser. Count risers for the number of steps you climb: the last riser takes you onto the upper floor.
Should I round to more risers to make them shorter?
You can. The calculator shows the fewest risers and what one or two more would give. Each extra riser makes every step a little lower and the stair a tread longer, so it comes down to the space you have.
Stair Calculator
Type the total rise and see risers, treads and the stringer drawn to scale. Landings and stringer layout come with Pro.