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Stair Stringer Calculator

Calculate stair stringer cuts for a deck or porch. Solve for risers, treads, stringer length, and angle with IRC R311.7 code compliance flags.

Stair stringer layout

Input mode

Top of upper floor to top of lower floor

Full horizontal run from the first riser to the upper landing

IRC max 7.75 in

IRC min 80 in

Stringer layout

16 risers, 15 treads

Riser height
6.75 in
Tread depth
8.8 in
Total run
132 in
Stair angle
39.29 deg
Stringer length
170.55 in
Notch depth
6.75 in
Remaining web (2x12)
5.89 in
2R + T
22.3 in

IRC R311.7 compliance

  • Riser <= 7.75 in
  • Tread >= 10 in
  • Headroom >= 80 in
Code and comfort notes
  • Tread depth 8.8 in is below the IRC R311.7.5.2 minimum of 10 in. Lengthen total run or remove a tread.
  • Stair angle 39.29 deg is outside the 30-37 deg comfortable band.
  • 2R + T = 22.3 in falls outside the 24-25 in stair-builder rule.

Stair Stringer Examples

Total rise15 risersStringer length with 140 in run
105 in7.00 in each175.00 in
112.5 in7.50 in each179.60 in
116.25 in7.75 in each181.97 in
90 in6.00 in each166.43 in
97.5 in6.50 in each170.61 in

Planning reference only. Verify riser, tread, landing, and stringer requirements with local code before cutting material.

Frequently Asked Questions about the Stair Stringer Calculator

What is a stair stringer?
A stair stringer is the diagonal member that supports treads and risers. The required material, number, spacing, connections, and support depend on stair width, tread system, loads, lumber, span, manufacturer instructions, and local code. Use the calculator for layout geometry, not structural approval.
How do I figure out how many risers I need?
Divide your total rise by your preferred riser height and round up. For a 108 in rise with a 7 in preferred riser, ceil(108 / 7) is 16 risers, which gives an actual riser height of 6.75 in. The number of treads is always one less than the risers on an open stringer, so 16 risers means 15 treads.
What is the IRC limit on riser height and tread depth?
IRC 2021 R311.7.5.1 caps residential riser height at 7.75 in. R311.7.5.2 sets the minimum tread depth (nose to nose) at 10 in. The variance between the tallest and shortest riser on the same flight cannot exceed 3/8 in. The calculator flags any output that breaks these limits.
How long does my stringer board need to be?
The stringer is the hypotenuse of the rise/run right triangle, so its length is sqrt(rise squared plus run squared). For a 108 in rise and 132 in run, that comes out to about 170.55 in or just over 14 ft. Order at least one size up so you can scribe and trim the top and bottom cuts cleanly.
Why does the calculator show remaining stringer web?
The remaining web is the wood left between the deepest notch and the back edge. The calculator flags less than 5 in as a planning warning, but IRC R311.7.3 does not establish a universal 5 in stringer-web rule. Have the stringer size, span, species, grade, cuts, and support checked for the actual stair.

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