Easy Wood Calc

Stairs for a 9 ft (108 in) total rise

Short answer

A 9 ft (108 in) total rise needs 14 risers of 7-11/16 inches and 13 treads. At 10 inches per tread the run is 130 inches (10 ft 10 in) and each stringer is about 169 inches (14 ft 1 in) long.

How to work it out

  1. 108 in ÷ 7.75 in max = 13.94 → round up to 14 risers, each 108 in ÷ 14 = 7-11/16 in strong (7.71 in)
  2. 13 treads × 10 in = 130 in run · √(108² + 130²) = 169 in along the slope
  3. Comfort check: 2 × 7-11/16 in + 10 in = 25.4 in (24–26 in is comfortable) · stair angle 37.6 degrees
  4. Throat: 11-1/4 in board − 6.11 in notch depth = 5-1/8 in
  5. Tread board: 10 in tread + 3/4 in nosing + 0 in riser board = 10-3/4 in
  6. Top level cut: 7-11/16 in riser + 1 in tread − 0 in top finish = 8-11/16 in below the upper subfloor

A 9 ft rise is common between floors of a house with 8 ft ceilings. Thirteen risers would be 8.3 in each — too steep — so the flight needs 14, and the stair sits right at the limit. A deeper tread or a landing makes it more comfortable if you have the space.

Adjust for your project

in
Straight down from the top walking surface to where the bottom step lands, finished surface to finished surface.
in
Depth of each notch you cut. 10 in minimum; 10½ in suits two 5/4×6 deck boards.
in
5/4 decking ≈ 1 in, 2× lumber = 1½ in
in
Outside to outside of the stringers. 36 in is the usual minimum.
in
Joist + subfloor + ceiling, e.g. 11¼ + ¾ + ½ = 12½ in. Gives the shortest opening that keeps 6 ft 8 in of headroom.
More options: Max riser · Spacing · Stringer board …
in
Most US codes: 7¾ in max. Leave it unless your inspector says otherwise.
in
DCA 6 (decks) allows up to 18 in for cut stringers; composite treads often need 12 in — check the tread maker.
in
A 2×12 is 11¼ in
Blank = the fewest risers under your maximum.
in
Level space from the top riser to the bottom one; the tread depth is worked out from it.
in
¾–1¼ in; 0 is allowed where treads are 11 in or deeper.
in
0 for open risers or none; ¾ in for 1× riser boards.
in
e.g. ¾ in hardwood. 0 if it is already down.
in
0 if it is already down.
Step-ups (risers)14 risers
Height of each step (mark this)7-11/16 in strong (7.71 in)
Steps to cut
13 steps to cut in each stringer + the upper floor is the top step
Total run (how far the stairs reach out)
130 in (10 ft 10 in)
Stringer length (along the slope)
169 in (14 ft 1 in)
Stringers needed
4 stringers
Stringer stock to buy
4 × 2×12 × 16 ft
Tread board depth to buy (tread + nosing + riser board)
10-3/4 in
Drop the stringer (trim off the bottom)
1 in
Top level cut, measured down from the top surface
8-11/16 in
Wood left below the notches (throat)
5-1/8 in
Shopping list
ItemWhat to buyNotes
Stringers4 × 2×12 × 16 ftStraight boards with no big knots along the bottom edge, where the wood is in tension.
Treads13 treads, each 36 in long × 10-3/4 in deepDepth = tread + nosing + riser board.
HardwareHangers or a hanger board at the top, fastened to the header or rim; screws for the treads and risersPlus a handrail on at least one side — four or more risers (2021 IRC R311.7.8).
Where to mark each step (height above the bottom)
Where to mark each step (height above the bottom)
StepHeight above the bottomGuard on open sides?
Tread 17-11/16 in—
Tread 215-7/16 in—
Tread 323-1/8 in—
Tread 430-7/8 inYes — over 30 in
Tread 538-9/16 inYes — over 30 in
Tread 646-5/16 inYes — over 30 in
Tread 754 inYes — over 30 in
Tread 861-11/16 inYes — over 30 in
Tread 969-7/16 inYes — over 30 in
Tread 1077-1/8 inYes — over 30 in
Tread 1184-7/8 inYes — over 30 in
Tread 1292-9/16 inYes — over 30 in
Tread 13100-5/16 inYes — over 30 in
Upper floor108 inYes — over 30 in
One step fewer or more
One step fewer or more
RisersEach stepTreadsTread depthTotal runCheck
13 risers8-5/16 in1210 in120 inRisers too tall
14 risers (shown)7-11/16 in1310 in130 inOK
15 risers7-3/16 in1410 in140 inOK
  • Each step is marked to the nearest 1/16 in. Stepping off 7-11/16 in 14 times would put the top 3/8 in low, so mark each step from the Where to mark each step table below instead.
  • Stair guard required from tread 4: it sits more than 30 in above the bottom, so open sides need a guard at least 34 in high (IRC R312.1.1, R312.1.2). This assumes the floor beside the stair is level with the bottom landing — measure where it falls away.
  • Headroom: keep at least 6 ft 8 in clear above the line of the nosings along the whole flight (IRC R311.7.2). Enter the upper floor thickness to get the shortest ceiling opening.
  • Leave a landing at the bottom (and the top, unless it is the floor itself) at least 36 in deep and as wide as the stair (IRC R311.7.6).
  • Trim 1 in off the bottom of each stringer (one tread thickness) so the first step comes out the same 7-11/16 in as the rest.
Check your codeCode limits vary by jurisdiction — confirm with your building department before you cut or build. (2021 IRC R311.7)

For this job · affiliate link
Stair gaugesYou are marking 13 identical notches on 4 stringers. Stair gauges locked on a framing square at 7-11/16 in and the tread depth make every one the same.
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Risers for a 108 in rise, by maximum riser height

Risers for a 108 in rise, by maximum riser height
Maximum riserStep-ups (risers)Riser height (decimal)Total run (how far the stairs reach out)Stringer length (along the slope)
7 in16 risers6.75 in150 in (12 ft 6 in)184-13/16 in (15 ft 4-13/16 in)
7.25 in15 risers7.2 in140 in (11 ft 8 in)176-13/16 in (14 ft 8-13/16 in)
7.5 in15 risers7.2 in140 in (11 ft 8 in)176-13/16 in (14 ft 8-13/16 in)
7.75 in14 risers7.71 in130 in (10 ft 10 in)169 in (14 ft 1 in)

What to know about stairs for a 9 ft rise

Fourteen risers of 7-11/16 in leave less than 1/16 in under the 7¾ in maximum in IRC R311.7.5.1, so there is no slack for measuring errors. If the finished floor at the top ends up ½ in thicker than you allowed, the top riser grows by that much — and the same section caps the difference between the tallest and shortest riser in a flight at ⅜ in. Measure after the subfloor is down, and add the finished flooring at both ends before you mark a stringer.

A rise of 108 in is still under the 151 in (12 ft 7 in) single-flight limit in R311.7.3, so a straight run is allowed, but it needs 130 in of floor — nearly 11 ft — plus 6 ft 8 in of headroom all the way down (R311.7.2). With 10 in treads, nosings of ¾ to 1¼ in are required.

Setting the maximum to 7½ in instead gives 15 risers of 7.2 in: one more tread and 10 in more run, but a flight with real margin under the limit. Either way the stringers are about 14.1 ft long, so the stock line asks for 16 ft 2×12s. Store and carry them flat — a long stringer with a 5.14 in throat can crack at a notch if it is levered off a truck by one end.

A foot lower, Stair stringers for an 8 ft rise has more room under the limit. Stair stringers for a 2.7 m rise is almost the same height in metric (108 in is about 2.74 m), and Stair stringers for a 10 ft rise is the next step up.

Different size? Use the full Stair Stringer Calculator.

What you’ll need

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Frequently asked questions

How many risers for a 108 in rise with a 7½ in maximum?

15 risers of 7-3/16 inches and 14 treads, for 140 inches (11 ft 8 in) of run at 10 inch treads — a flight that sits comfortably inside the 7¾ inch limit.

How long is the stringer for a 9 ft rise with 11 in treads?

About 179-3/16 inches (14 ft 11-3/16 in) along the slope, with 143 inches (11 ft 11 in) of run — 4 × 2×12 × 16 ft. The 11 inch tread removes the nosing requirement but adds about 13 inches to the footprint.

Other common sizes

Sources