Deck Stairs, 48 Inch Rise, Three-Stringer Layout
A low deck, 48 in to grade, hung with a dropped header.
Formula SSC-2026.1
IRC check pass
Risers / treads
7 / 6
Riser inside 4 to 7.75 in
Exact riser
6 7/8 in
174.2 mm
Total run
5 ft 6 in
1,676 mm
Stringer length
6 ft 8 3/4 in
Order 8 ft 2x12
Incline
36.03°
Square 6 7/8 in rise · 11 in run
Stringers @ 16 in
3
Throat 5.43 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 |
|---|---|---|---|---|---|
| 8 ft 2x12 | 7.30 ft cut | end cuts included | 3 boards | USD | $50.40 |
| Stringer delivery weight | 67 lb | — | 30 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 |
| 3 ft 6 in | 6 | 7 in | 5 | 4 ft 7 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 | 9 | 6 11/16 in | 8 | 7 ft 4 in | 10 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 Stairs, 48 Inch Rise, Three-Stringer Layout
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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
Forty-eight inches at a 7 in target gives a comfortable deck riser. The mount is dropped and the decking is 1.5 in, so the stringer layout rise is 46.5 in. The width is 36 in, which produces three stringers at 16 in on center. Treads are 11 in. If the throat warning appears, the notch is deep relative to a 2x12 and the stair wants a look from the inspector before you buy lumber.
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
- What does a dropped header change?
- The stringer rise subtracts the deck thickness so the board lands under the walking surface instead of running the full floor-to-floor rise.
- Why three stringers?
- A 36 in width at 16 in on center is two spaces plus the end board, which is three stringers.
- What stock 2x12 do I pick up?
- The result names the next stock length that covers the diagonal plus end-cut waste. If it says over 24 ft, the stair needs a splice or an engineered stringer.