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

Tread depth (cm)

Tread depth in centimeters between 20 and 35.

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

Recommended string thickness in millimeters, 45 at 26 cm tread depth or deeper, otherwise 40.

• 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.

• Tread Thickness Rule

  Recommend a stair tread thickness of 40 millimeters for string spans up to 90 centimeters and 50 millimeters beyond.

• Tread Depth Check

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

• Treppen Bequemlichkeitsregel

  Compute the German stair comfort-rule dimension as tread going minus riser height; interpret it as a planning metric, not proof of code compliance.