Deck Stair Stringer Calculator, 36 to 96 Inch Rise
A 72 in deck rise as the working case, compared with 36 through 96 in.
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
8 ft 3 in
2,515 mm
Stringer length
10 ft 2 7/16 in
Order 12 ft 2x12
Incline
36.03°
Square 7 3/16 in rise · 11 in run
Stringers @ 16 in
3
Throat 5.23 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 | 10.80 ft cut | end cuts included | 3 boards | USD | $75.60 |
| Stringer delivery weight | 101 lb | — | 46 kg | 2.8 lb/ft planning weight | — |
| Total rise | Risers | Exact riser | Treads | Run | 2x12 stock | Check |
|---|---|---|---|---|---|---|
| 3 ft 0 in | 5 | 7 3/16 in | 4 | 3 ft 8 in | 8 ft | Pass |
| 4 ft 0 in | 7 | 6 7/8 in | 6 | 5 ft 6 in | 8 ft | Pass |
| 5 ft 0 in | 8 | 7 1/2 in | 7 | 6 ft 5 in | 10 ft | Pass |
| 6 ft 0 in | 10 | 7 3/16 in | 9 | 8 ft 3 in | 12 ft | Pass |
| 7 ft 0 in | 12 | 7 in | 11 | 10 ft 1 in | 14 ft | Pass |
| 8 ft 0 in | 13 | 7 3/8 in | 12 | 11 ft 0 in | 16 ft | Pass |
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: Deck Stair Stringer Calculator, 36 to 96 Inch Rise
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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 working rise is 72 in, the target riser is 7.25 in, and the tread is 11 in, which is a comfortable deck stair. The comparison table repeats 36, 48, 60, 72, 84, and 96 in so you can see when the riser crosses 7.75 in. Stringers are counted at 16 in on center across a 36 in width, which is three boards. A dropped mount is available if the deck band hides the top of the stringer. The throat estimate assumes a 2x12.
Code reference
IRC R311.7.5.1 limits risers to 7.75 in and R311.7.5.2 requires at least a 10 in tread. Confirm local amendments, guards, and headroom.
Field questions
- How many stringers are on a 36 inch deck stair?
- Width divided by 16 in, rounded down, plus one, with a minimum of two. A 36 in stair is three stringers.
- What rise still passes the IRC check?
- Each row shows Pass or Warning. A warning means the equal riser is over 7.75 in or under 4 in, or the tread is under 10 in.
- What lumber length should I buy?
- The diagonal plus one riser of end waste is matched to the next stock length from 8 ft through 24 ft.