Stair stringer calculator: rise, run and cuts

How it works

Enter a proposed number of risers as well as the measured dimensions. Select British Columbia 2024 private stairs to check the listed rise and going ranges. Vancouver, federal lands, Ontario, other provinces and other code editions remain geometry-only. Confirm the applicable permit edition locally.

Formula

• Divide the rise into equal steps

  Riser = total rise ÷ proposed number of risers

  Enter the proposed riser count. In the supported BC reference, each rise is checked from 125 to 200 mm and each going from 255 to 355 mm.

• Divide the run between risers

  Goings = risers − 1, going = total run ÷ goings

  Run is measured between first and last riser faces. Landing dimensions are not included.

• Check the step-line pitch

  Pitch = arctan(riser ÷ going)

  This angle describes the repeating step geometry, no Canadian code pitch check is applied.

• Estimate the stringer line

  Stringer length = √(total rise² + total run²)

  This theoretical length excludes end cuts, overhangs and waste.

• Adjust the bottom seat

  Bottom seat rise = calculated riser − tread thickness

  The cut-layout adjustment accounts for the lowest tread thickness.

Worked example

1. 1

   Enter an example geometry

   Rise 2,700 mm · run 3,600 mm · 15 risers · tread 25 mm

   For imperial input, choose inches, results still display in millimetres for easy comparison.

2. 2

   Read the geometry estimate

   15 risers at 180 mm · 14 goings at 257.1 mm

   For the named BC 2024 private-stair reference, 180 mm rise and 257.1 mm going pass the two listed dimensional ranges. This does not approve the complete stair or another jurisdiction.

3. 3

   Plan stringer stock

   Stringer line = 4,500 mm · bottom seat rise = 155 mm

   Choose longer stock to allow trimming and layout waste, then have the stair checked locally.

Assumptions and limits

The supported reference is British Columbia Building Code 2024 Tables 9.8.4.1 and 9.8.4.2 for private stairs, cross-checked against the BC Government code dataset on October 15, 2026. It covers rise 125 to 200 mm and rectangular going 255 to 355 mm. Vancouver, federal lands and other provinces have separate requirements. Headroom, landings, uniformity, flight height, handrails, guards, loads and structural details are not checked by these two dimensional tests. A geometry estimate is not a structural stringer design or permit assessment.

Frequently asked questions