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

Stock Thickness Millimeters (mm)

Required number input.

Fit Clearance Millimeters (mm)

Required number input.

One-third-rule tongue thickness from stock thickness and groove width after a user-selected fitting clearance. 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]

Tongue Thickness Millimeters (mm)

The resulting tongue thickness millimeters returned as a number.

Groove Width Millimeters (mm)

The resulting groove width millimeters returned as a number.

• 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.

• Tongue Groove Clearance Calculator

  Compute the groove width for a tongue joint by adding a 0.2 mm fitting clearance to the tongue thickness.

• Schlitz Zapfen Masse 1 3 Regel

  One-third-rule tenon thickness and equal shoulder widths from stock thickness; these are starting dimensions, not a strength check.

• Tongue Thickness

  Find tongue thickness from mating groove width after subtracting an explicit total fit clearance.