Measure the height the stairs climb. You get how many steps, how tall and deep each one is, the room the stair takes, whether it meets the code, the stairwell opening for headroom and the stringer to buy.
Your stairs
14 risers of 7¹¹⁄₁₆″ on 13 treads11′ 5″ of run at 36.3° · meets the IRC · a stairwell opening 10′ 3″ long for 6′ 8″ of headroom
Quick answer: divide the total rise by 7¾″ (the home code’s tallest riser) and round up: that is the fewest risers. A 9′ (108″) floor-to-floor rise takes 14 risers of 7¹¹⁄₁₆″ and 13 treads; on 10½″ treads that is 11′ 5″ of run, plus a 36″ landing at the bottom. Treads are 10″ deep at least, and the stair needs 6′ 8″ of headroom over the nosings.
How to use the stair calculator
- Measure the total rise: from the finished lower floor (or the ground) to the finished upper floor (or the deck’s surface), straight up.
- Pick a tread depth, measured nosing to nosing: 10″ is the home code’s least, 11″ a public building’s.
- Indoors? Enter the upper floor’s thickness (joists, subfloor and ceiling) to get the stairwell opening that keeps the headroom.
- Short of room? Enter the floor from the top step to the wall in front of the stair, and the calculator says whether the stair and its bottom landing fit.
- You get the risers, treads, run and angle, the code’s verdict, every other riser count beside it, the stringer to buy and its first cut, drawn to scale. Type a riser count to try a gentler stair.
The rules behind the numbers
Risers and treads
“The riser height shall be not more than 7 3/4 inches (196 mm)” and “The tread depth shall be not less than 10 inches (254 mm)”, measured from nosing to nosing (IRC R311.7.5.1, R311.7.5.2). Within a flight the tallest riser may beat the shortest by ⅜″ at most, and the same for treads, so divide the whole rise evenly. Treads under 11″ deep get a nosing ¾–1¼″ (R311.7.5.3). California’s residential code says the same. In public buildings, risers are 4–7″ and treads 11″ at least (IBC 1011.5.2).
Headroom
“The headroom in stairways shall be not less than 6 feet 8 inches (2032 mm) measured vertically from the sloped line adjoining the tread nosing” (R311.7.2); 80″ in a public building (IBC 1011.3). Under the upper floor that decides how long the stairwell opening must be: it reaches back from the top step until the floor’s underside is 6′ 8″ above the nosing line.
Flights and landings
“A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings” (R311.7.3; 12′ in a public building, IBC 1011.8). There is a floor or landing at the top and bottom of every stair, as wide as the stair and, on a straight run, at least 36″ deep (R311.7.6). The stair is 36″ wide at least (R311.7.1), and four or more risers take a handrail (R311.7.8).
Steps by height
The fewest risers the home code allows, on 10½″ treads; the opening is for a 10″ upper floor:
| Total rise | Risers | Each riser | Treads | Run | Stairwell opening |
|---|---|---|---|---|---|
| 24″ (a deck) | 4 | 6″ | 3 | 2′ 8″ | — |
| 30″ (a deck) | 4 | 7¹⁄₂″ | 3 | 2′ 8″ | — |
| 36″ (a deck) | 5 | 7³⁄₁₆″ | 4 | 3′ 6″ | — |
| 48″ (a deck) | 7 | 6⁷⁄₈″ | 6 | 5′ 3″ | — |
| 96″ (8′) | 13 | 7³⁄₈″ | 12 | 10′ 6″ | 10′ 8″ |
| 102″ (8′ 6″) | 14 | 7⁵⁄₁₆″ | 13 | 11′ 5″ | 10′ 10″ |
| 108″ (9′) | 14 | 7¹¹⁄₁₆″ | 13 | 11′ 5″ | 10′ 3″ |
| 114″ (9′ 6″) | 15 | 7⁵⁄₈″ | 14 | 12′ 3″ | 10′ 5″ |
| 120″ (10′) | 16 | 7¹⁄₂″ | 15 | 13′ 2″ | 10′ 6″ |
Home and public stairs
| Home (IRC) | Public building (IBC) | |
|---|---|---|
| Riser | 7¾″ at most | 4–7″ |
| Tread | 10″ at least | 11″ at least |
| Headroom | 6′ 8″ | 80″ (6′ 8″) |
| Rise of one flight | 12′ 7″ at most | 12′ at most |
| Landing depth | 36″ on a straight run | the stair’s width, 48″ at most needed |
| Width | 36″ | 44″ (36″ under 50 people) |
Four worked examples
Basement stairs, 9′ floor to floor. 14 risers of 7¹¹⁄₁₆″ on 13 treads of 10½″: 11′ 5″ of run at 36.3°. Under a 10″ floor the stairwell opening runs 10′ 3″ back from the top step. The stringer is 15′ 3″ along the steps: a 16-ft board, with 1″ cut off its foot for the treads.
A deck 36″ off the ground. 5 risers of 7³⁄₁₆″ on 4 treads of 11″: 3′ 8″ of run, and with a 36″ landing at the bottom, 6′ 8″ of yard. Five risers take a handrail.
The same basement stairs with 12′ 6″ of room. The run and its landing need 14′ 5″: 1′ 11″ too long, and even 10″ treads do not fit it. Turn the stair with a landing, as an L or a U.
A shop’s stairs, 9′ floor to floor. Public stairs are 7″ at most: 16 risers of 6³⁄₄″ on 15 treads of 11″, 13′ 9″ of run.
Common stair mistakes
- Measuring the rise before the flooring goes down. Measure finished floor to finished floor, or the first and last steps come out uneven.
- A short last step. Divide the whole rise evenly; risers in a flight may differ by ⅜″ at most.
- Forgetting the landing. A stair needs 36″ of floor at its foot, so it takes more room than its run.
- Cutting every step on the stringer the same. The treads add their thickness on top, so the first step is cut that much shorter.
- A stairwell opening that is too short. Headroom is measured over the nosings all the way up: a 10″ floor needs an opening about 10′ long.
Your building department has the last word, and a stair usually needs a permit. Add the handrail and the guard with the railing height and baluster spacing calculator, plan a ramp beside it with the wheelchair ramp calculator, and draw the rooms in the free 2D planner.
Railing & balustersRead next
- Interior staircase design
- DIY outdoor stairs
- Front porch stair ideas
- Stair railing ideas
- Under stairs storage
Stair rise and run questions
What is the standard stair rise and run?
At a house, risers 7¾″ at most and treads 10″ at least, nosing to nosing (IRC R311.7.5); in a public building, risers 4–7″ and treads 11″ at least (IBC 1011.5.2). Every riser and tread in a flight matches within ⅜″.
What is the standard stair riser height?
7¾″ is the most the home code allows (R311.7.5.1). Divide your total rise by 7¾″ and round up for the fewest risers: a 108″ rise takes 14 risers of 7¹¹⁄₁₆″.
What is the standard stair tread depth?
10″ at least at a house, measured horizontally from one nosing to the next (R311.7.5.2), and 11″ in a public building. Below 11″ the tread needs a nosing of ¾–1¼″ (R311.7.5.3).
How do I calculate stairs for a deck?
Measure from the deck’s surface to the ground where the stair will land, divide by 7¾″ and round up for the risers; the treads are one fewer. A 36″ deck takes 5 risers of 7³⁄₁₆″ and 4 treads; on 11″ treads that is 3′ 8″ of run, plus a 36″ landing at the foot.
How long is a stair stringer?
Along the corners of the steps, from the floor to the top, it is the number of risers × √(riser² + tread²): 15′ 3″ for 14 risers of 7¹¹⁄₁₆″ on 10½″ treads, so a 16-ft board.
How much headroom does a stair need?
6′ 8″ measured straight up from the line over the nosings (R311.7.2), the whole way up. Under a 10″ upper floor that makes the stairwell opening about 10′ long for a 9′ stair.
What is the average staircase height?
A staircase climbs one storey, finished floor to finished floor: with 8′ ceilings and a 10–12″ floor between, that is 106–108″, which takes 14 risers by the home code.