Stair Stringer Layout Calculator
Turn a floor-to-floor rise into an equal riser, a total run, a diagonal stringer, and the framing-square settings.
Formula SSC-2026.1
IRC check pass
Risers / treads
10 / 9
Riser inside 4 to 7.75 in
Exact riser
7 3/16 in
182.9 mm
Total run
7 ft 10 1/2 in
2,400 mm
Stringer length
9 ft 10 13/16 in
Order 12 ft 2x12
Incline
37.30°
Square 7 3/16 in rise · 10 1/2 in run
Stringers @ 16 in
3
Throat 5.31 in on a 2x12
Rise, run, and the incline are scaled from the live riser and tread. Framing-square gauges match the exact riser and the tread depth.
| Item | Net | Waste | Order | Unit price | Line total |
|---|---|---|---|---|---|
| 12 ft 2x12 | 10.50 ft cut | end cuts included | 3 boards | USD | $75.60 |
| Stringer delivery weight | 101 lb | — | 46 kg | 2.8 lb/ft planning weight | — |
| Target | Risers | Exact riser | Run | Angle | Check |
|---|---|---|---|---|---|
| 7 in | 10 | 7 3/16 in | 7 ft 10 1/2 in | 37.3° | Pass |
| 7 1/4 in | 10 | 7 3/16 in | 7 ft 10 1/2 in | 37.3° | Pass |
| 7 1/2 in | 10 | 7 3/16 in | 7 ft 10 1/2 in | 37.3° | Pass |
| 7 3/4 in | 9 | 8 in | 7 ft 0 in | 40.6° | Warning |
Show the deterministic formula
Risers = round(total rise ÷ target rise). Exact riser = total rise ÷ risers, reported to the nearest 1/16 in and in millimeters. Treads = risers − 1. Total run = treads × tread depth.
Diagonal = hypotenuse of stringer rise and total run. A dropped header uses total rise minus landing thickness. Stock is the next 8, 10, 12, 14, 16, 18, 20, or 24 ft board.
Stringers = floor(width ÷ 16) + 1, with a minimum of 2. Throat ≈ 11.25 − (riser × tread) ÷ hypotenuse.
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Project: Stair Stringer Layout Calculator
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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.
Engineering notes
The riser count is the total rise divided by the target rise, rounded to the nearest whole riser. Every riser is then the same height, so the layout variation is zero before field error. Treads are one fewer than risers for a stair between two levels. Total run is tread count times tread depth. The diagonal is the hypotenuse of the stringer rise and the total run.
A dropped header subtracts the deck or landing thickness from the stringer rise so the board lands under the walking surface. Throat is estimated on a 11.25 in 2x12. Stringers are placed at 16 in on center, with one at each side.
Code reference
IRC R311.7.5.1 maximum 7.75 in riser and R311.7.5.2 minimum 10 in tread depth. Riser-to-riser variation in the code is 3/8 in; this layout divides the rise equally. Confirm local amendments and guards.
Field questions
- Why is the tread count one less than the riser count?
- The upper floor is the last riser. A stair from a lower floor to an upper floor has one more riser than the number of treads you cut into the stringer.
- What should I set on the framing square?
- Set the rise gauge to the exact individual riser and the run gauge to the tread depth. Both are shown on the blueprint after you change the inputs.
- What if the riser is over 7.75 inches?
- The badge turns to a warning and the result shows the riser count that would land at or under 7.75 inches. Add that riser and shorten the target, then recheck headroom and the total run.