Use this workshop calculation to turn measured dimensions and the selected construction convention into a cut, spacing, fit, or material-planning value.

Span between strings (cm)

Span between the strings in centimeters, up to 200.

Recommend a stair tread thickness of 40 millimeters for string spans up to 90 centimeters and 50 millimeters beyond. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Recommended tread thickness (mm)

Recommended tread thickness in millimeters, 40 for spans of at most 90 centimeters, otherwise 50.

• Nominal dimensions, kerf, moisture movement, hardware clearances, wall squareness, and manufacturer instructions can change the required shop dimension. Measure the actual assembly and test critical joints on scrap before cutting finished material.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Complement the calculated dimension with a physical story stick, dry fit, or full-size layout. Follow the hardware, coating, adhesive, or machine manufacturer's limits where they differ from a rule of thumb.

• String Thickness Rule

  Recommend a stair string thickness of 45 millimeters for tread depths of 26 centimeters or more and 40 millimeters below.

• Stair Run Length Calculator

  Compute the total stair run in centimeters as the tread depth times the number of steps minus one.

• Tread Depth Check

  Check whether a stair tread depth falls in the ideal 28 to 29 cm range and report its deviation in centimeters.