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MaterialCalc — Stair Stringer Layout Calculator

Estimate prepared 09/01/2026. Estimates only; verify against your plans before ordering.

Stair Stringer Layout Calculator

Finished floor to finished floor, or deck surface to grade.

Ten inches is the code minimum. Eleven feels much better.

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Result

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Stair layout is one division and one square root, but getting the riser height wrong by an eighth of an inch across a flight is what makes stairs feel wrong to walk on and fail inspection. This gives you the exact riser height, the total run, the stringer length to cut from, and the lumber to buy.

Assumptions used

These are the numbers behind the result. Where one of them is soft, the cost range widens rather than pretending to a precision the data does not have.

Maximum stair riser
7.75 in

International Residential Code (2021) — Published product data, checked 09/01/2026

Minimum stair tread depth
10 in

International Residential Code (2021) — Published product data, checked 09/01/2026

Prices verified 09/01/2026 (US national average, big-box retail shelf price and regional ready-mix quotes). Regional adjustment: Blended from RSMeans city cost index bands and BLS construction wage differentials.

The formula

Risers = total rise ÷ 7.75 in maximum, rounded up. Actual riser height = total rise ÷ riser count, which makes every riser identical. Treads = risers − 1. Total run = treads × tread depth. Stringer length = the hypotenuse: the square root of rise squared plus run squared.

Worked examples

108 in rise, standard interior flight

Total rise: 108 Tread depth: 10.5 Stair width: 36 Waste: 10

14 risers at exactly 7-11/16 in, 13 treads, 136.5 in of run and a stringer just over 14 ft. Comfortably inside code and fits a 16 ft board.

48 in rise from a deck to grade

Total rise: 48 Tread depth: 11 Stair width: 48 Waste: 10

7 risers at 6-7/8 in — shallower than an interior stair, which is normal outdoors. The 48 in width calls for four stringers.

145 in rise in an older house

Total rise: 145 Tread depth: 10 Stair width: 36 Waste: 10

19 risers at 7.63 in. Over 12 ft of rise, so this flight needs an intermediate landing and cannot be cut from a single board.

Choosing materials

  • Cut one stringer, set it in place and check it against the actual opening before cutting the others. Every stair opening is slightly out of what the drawing says.
  • Remember to drop the bottom of the stringer by the thickness of one tread. Skip this and the bottom riser is a tread thicker than every other one, which is both a trip hazard and an automatic inspection failure.
  • Use 2x12 stock. After the notches are cut, the remaining throat on a 2x12 is about 5 in, which is the minimum most codes accept. A 2x10 leaves too little.
  • Three stringers is adequate up to 36 in wide. Beyond that, or with thin treads, go to four — the bounce in the middle of a wide two-stringer tread is unmistakable underfoot.
  • Above 12 ft of total rise the code requires an intermediate landing, and a stringer that long will not come out of a single 16 ft board anyway.

Common questions

How do I calculate stair stringers?

Divide the total rise by 7.75 in and round up to get the riser count. Divide the total rise by that count for the exact riser height. Treads are one fewer than risers. Total run is treads times tread depth, and the stringer is the hypotenuse of rise and run.

What is the maximum riser height?

The IRC allows 7.75 in for residential stairs, with a minimum 10 in tread. Risers within a flight must not vary by more than 3/8 in. Commercial codes are stricter — typically 7 in maximum riser and 11 in minimum tread.

What size lumber for stair stringers?

2x12. Once the treads and risers are notched out, the remaining throat must be at least 5 in in most jurisdictions, and only a 2x12 leaves that much. Pressure-treated 2x12 for anything outdoors.

How many stringers do I need?

Three for stairs up to 36 in wide, four up to 48 in, and one more for every additional 16 in of width. Composite or thin treads need closer spacing than solid wood does.

Why do I drop the bottom of the stringer?

Because the bottom step gains a tread thickness that the others do not. Cut the bottom of the stringer down by the tread thickness, and every riser in the flight ends up equal — which is what the code requires and what your feet expect.

How long a stringer can I cut from one board?

A 16 ft 2x12 gives you a stringer covering roughly 11 ft of rise at a normal pitch. Anything longer needs a landing, which the code requires above 12 ft of total rise regardless.

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