How to Calculate, Lay Out and Cut Stair Stringers

Divide the total rise by the largest riser and round up to whole risers, divide the rise by that count for the riser height, then find the stringer as the long side of a right triangle and mark every step from the whole rise.

Estimates for planning, not professional advice. Read the full notice.

Work it out for your own sizes

Calculate your stair

Example to try: Total rise 8 ft 1 1/2 in, Tread run (this example's own size) 10 in, Tread thickness (this example's own size) 1 in

Step by step

  1. Measure the total rise

    Measure from the finished floor at the bottom to the finished floor at the top. In this example the total rise is 8 ft 1 1/2 in, typed as feet and inches.

  2. Divide by the largest riser

    Divide the total rise by the largest riser you will allow. Here that is 8 ft 1 1/2 in divided by 7.75 in[1], the model-code value quoted below. The answer has a fraction.

  3. Round up to whole risers

    Round the answer up to a whole number, because rounding down would leave every riser taller than the largest you allowed. The example comes to 13 risers.

  4. Find the riser height and the treads

    The riser height is the total rise divided by the risers: 7 1/2 in. The floor above is the top tread, so there is one tread fewer than risers: 12 treads.

  5. Work out the total run

    The total run is the treads times the tread run. With a tread run of 10 in the example runs 10 ft.

  6. Work out the stringer length

    The stringer is the long side of a right triangle. Its short sides are the rise below the top riser, 7 ft 6 in, and the total run, 10 ft, which give 12 ft 6 in. After your cut allowance, choose the shortest board that is long enough: 14 ft in the listed lengths.

  7. Set the framing square

    Set the riser height, 7 1/2 in, on the tongue and the tread run, 10 in, on the blade, with both marks on the edge of the board. The blade then lies at 36.87 degrees to the edge of the board, which is the slope of the stair, and the square steps along the board with the same two settings.

  8. Take the drop off the bottom

    Cut the bottom of the stringer shorter by the riser height less the tread thickness. With a tread thickness of 1 in, the drop is 6 1/2 in, and the first step comes out the same height as the others.

  9. Mark every step from the whole rise

    Mark each riser from the whole rise, one at a time: each mark is the total rise times its riser number divided by the risers. Adding the rounded riser height again and again lets rounding build up, and the last mark would miss the whole rise. Here the last riser mark is 8 ft 1 1/2 in, the total rise itself.

Layout marks for this stair

Where to mark each riser and each tread, measured from the floor and from the first riser

MarkReads
Riser 1, from the floor 7 1/2 in
Riser 2, from the floor 1 ft 3 in
Riser 3, from the floor 1 ft 10 1/2 in
Riser 4, from the floor 2 ft 6 in
Riser 5, from the floor 3 ft 1 1/2 in
Riser 6, from the floor 3 ft 9 in
Riser 7, from the floor 4 ft 4 1/2 in
Riser 8, from the floor 5 ft
Riser 9, from the floor 5 ft 7 1/2 in
Riser 10, from the floor 6 ft 3 in
Riser 11, from the floor 6 ft 10 1/2 in
Riser 12, from the floor 7 ft 6 in
Riser 13, from the floor 8 ft 1 1/2 in
Tread 1, from the first riser 10 in
Tread 2, from the first riser 1 ft 8 in
Tread 3, from the first riser 2 ft 6 in
Tread 4, from the first riser 3 ft 4 in
Tread 5, from the first riser 4 ft 2 in
Tread 6, from the first riser 5 ft
Tread 7, from the first riser 5 ft 10 in
Tread 8, from the first riser 6 ft 8 in
Tread 9, from the first riser 7 ft 6 in
Tread 10, from the first riser 8 ft 4 in
Tread 11, from the first riser 9 ft 2 in
Tread 12, from the first riser 10 ft

Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.

Each mark is worked out from the whole rise or run, then written to the nearest sixteenth of an inch. Marks are never added up from the rounded riser height, which would drift.

This stair beside the 2021 IRC values

The example's riser, tread, total rise, risers and tread depth beside the quoted model-code values

ItemThis exampleModel-code value
Riser height: within the 2021 IRC value 7 1/2 in 7.75 inModel-code (2021 IRC R311.7.5.1) maximum stair riser height; local adopted codes differ.
Tread depth: within the 2021 IRC value 10 in 10 inModel-code (2021 IRC R311.7.5.2) minimum stair tread depth; local adopted codes differ.
Total rise of the flight: within the 2021 IRC value 8 ft 1 1/2 in 12 ft 7 inModel-code (2021 IRC R311.7.3) maximum vertical rise of a flight of stairs; local adopted codes differ.
Risers in the flight 13 risers 4 risersModel-code (2021 IRC R311.7.8) number of risers in a flight for which the 2021 IRC lists a handrail on one side; local adopted codes differ.
Tread depth, for the nosing exception 10 in 11 inModel-code (2021 IRC R311.7.5.3) tread depth from which the 2021 IRC text sets no nosing projection; local adopted codes differ.

Source: 2021 International Residential Code, Chapter 3 Building Planning, International Code Council, 2021 IRC, checked Nov 12, 2026.

A row reads within, outside or at the quoted value. Where the quoted value is a threshold, a row shows the quote alone. These are model-code values; the code your area has adopted may differ.

In the 2024 IRC these provisions are in Sections R318.7 (stairways) and R321 (guards). The 2024 chapter.

Worked example: a staircase stringer

Show the working
  1. Risers: divide the total rise by the largest riser, then round up 8 ft 1 1/2 in ÷ 7.75 in[1] = 13 risers
  2. Riser height: the total rise divided by the risers 8 ft 1 1/2 in ÷ 13 risers = 7 1/2 in
  3. Total run: the treads times the tread run 12 treads × 10 in = 10 ft
  4. Rise below the top riser: the total rise less one riser 8 ft 1 1/2 in − 7 1/2 in = 7 ft 6 in
  5. Stringer before cut allowance: the long side of a right triangle whose short sides are that rise and the total run 7 ft 6 in = 12 ft 6 in
  6. Cut allowance: add what you allow for the end cuts 12 ft 6 in + 0 in = 12 ft 6 in
  7. Bottom drop: the riser less the tread thickness 7 1/2 in − 1 in = 6 1/2 in

Questions

How do I find the length of a stair stringer?

Treat the rise below the top riser and the total run as the two short sides of a right triangle. The stringer is its long side, and you add whatever you allow for the end cuts before choosing a board.

Why do I round the number of risers up?

Dividing the total rise by the largest riser rarely gives a whole number. Rounding down would leave every riser taller than the largest you allowed, so any fraction means one more riser, and the riser height is then the total rise divided by that count.

How do I use the framing square settings?

Set the riser height on the tongue and the tread run on the blade, then mark along both edges. Slide the square along the board and mark every step from the same two points.

Why do I cut the bottom of the stringer shorter?

The first tread adds its own thickness on top of the cut. Taking the tread thickness off the first riser height makes the first step come out the same height as the others.

Calculate it for your project

Enter your own sizes to get the amount to buy or the layout figures, with the working shown and a page to print.

Work out your own stringer

Local codes and amendments differ; your building department decides.

Sources (1)
  1. 2021 International Residential Code, Chapter 3 Building Planning, International Code Council, 2021 IRC. Code or government
    “The riser height shall be not more than 7 3/4 inches (196 mm).”
    “The tread depth shall be not less than 10 inches (254 mm).”
    “A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings.”
    “Handrails shall be provided on not less than one side of each flight of stairs with four or more risers.”
    “A nosing projection is not required where the tread depth is not less than 11 inches (279 mm).”
    Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used

These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.

Made with HoneyDoMath.com. Estimates for planning; check product labels and local codes before you buy or build.