Stair Stringer Calculator

Lay out a cut stair stringer: rise and run per step, stringer length, notch depth, throat and board length, with a side-view diagram.

A cut stringer is the sloping board the treads sit on, with a notch for every step. Its length is the hypotenuse of the stair's total rise and total run: for a 108 in rise with 14 risers of 7.71 in and 13 treads of 10½ in, that's √(108² + 136.5²) = 174 in, about 14½ ft, so you'd cut it from a 16 ft board. Each notch takes a bite out of the board: measured square to the edge it's 6.2 in deep here, which leaves a throat of about 5 in in a 2 × 12 (11¼ in). Enter the rise, riser limit and going, and this calculator gives the stringer length, board length, notch depth, throat and the number of stringers for your stair width, with a side-view drawing.

Units
Building code
in
in
in
in
in
in
Stringer length
14.5 ft

buy 16 ft boards × 4

Risers
14 × 7.714 in

13 treads of 10.5 in

Throat
5.033 in

notch 6.217 in deep

Angle
36.3°

2R + G 25.93 in

Checked against International Residential Code (US)

  • Passes: Riser at most 7.75 in
  • Passes: Going (tread) at least 10 in
total run 136.5 inrise 108 in
The stringer cut from a 11.25 in board: 14 risers, 13 treads. Not to scale for very long flights.
How it was worked out
  1. 108 in total rise ÷ 7.75 in maximum riser = 13.94, rounded up to 14 risers of 7.714 in
  2. 14 risers need 13 treads (the top floor is the last step): 13 × 10.5 in = 136.5 in total run
  3. Stringer line length = √(rise² + run²) = 14.5 ft (174.1 in); buy at least 16 ft to allow for the top and bottom cuts
  4. Angle = tan⁻¹(7.714 in ÷ 10.5 in) = 36.3°; 2 × riser + going = 25.93 in
  5. Each notch is 6.217 in deep (square to the edge), leaving a throat of 5.033 in in a 11.25 in board
  6. Stringers: 36 in wide at 16 in spacing = 4 stringers

The checks cover the main rise and going limits for stairs in a house; headroom (6 ft 8 in), handrails, guards, winders and landings have rules too, and local codes can differ. Measure the total rise from finished floor to finished floor.

Common use cases

  • Lay out and cut stringers for deck or porch steps
  • Choose a board length before buying lumber
  • Check there's enough throat left after notching
  • Work out how many stringers a wide stair needs

How to use

  1. Choose your units and building code.
  2. Enter the total rise, the maximum riser and the going.
  3. Enter the stair width, stringer spacing and the depth of the board you'll cut from.
  4. Read the stringer length, board to buy, notch depth and throat, and check the drawing.

FAQ

How long should a stair stringer be?

At least the length of the line from the bottom of the first riser to the top landing: √(total rise² + total run²). Buy a board a foot or so longer for the top and bottom cuts and any connection hardware.

What is the throat of a stringer?

The solid wood left between the inside corner of each notch and the bottom edge of the board. Deeper notches leave less, which is why stringers are usually cut from 2 × 12s. Check your local code or deck guide for the minimum it requires.

How many stringers do I need?

That depends on the tread material and how far it can span. Wood treads are commonly supported every 16 in (400 mm) or so, and composite treads often need closer stringers. Set the spacing to suit your treads and the calculator counts them.

Related tools

Results are estimates for planning and buying materials, worked out from the figures you enter and typical values (weights, coverage, sizes) that vary by product and supplier. They are not engineering, building or professional advice. Check your local building code, the product maker's instructions and your supplier's figures before you buy or build, and use a qualified professional for structural, electrical and gas work. The code checks cover the main dimensions only; the rules where you live, and your building inspector, have the final say.