Laser Kerf Explained: How to Measure and Compensate for It

Kerf is the width of material your laser burns away as it cuts. It is tiny, usually a fraction of a millimetre, but it decides whether a box slides together snugly or falls apart. Here is how to measure it on your own machine and what to do with the number.

What kerf is and why it matters

A laser beam has width. As it cuts, it vaporises a thin channel of material, so every piece comes out very slightly smaller than the drawn line and every slot comes out slightly wider. On flat designs such as ornaments or signs you will never notice. On slotted projects such as boxes, stands and 3D models, kerf decides how tight the joints are.

Kerf depends on your setup

There is no single correct kerf value. It changes with the type of laser, the lens and focus, power and speed settings, and the material itself. As a rough guide, kerf in 3 mm plywood or MDF is often somewhere between 0.1 and 0.2 mm, but your machine may differ. The only reliable number is the one you measure.

How to measure your kerf in five minutes

1. Draw a rectangle exactly 50 mm wide in your laser software.
2. Cut it from the material you plan to use, with your normal cut settings.
3. Measure the cut-out piece with digital calipers.
4. Subtract the measured width from 50 mm. That difference is your kerf. For example, if the piece measures 49.84 mm, your kerf is 0.16 mm.

Repeat the test whenever you change material, lens or focus height.

Using kerf offset in LightBurn

LightBurn has a Kerf Offset setting in the cut layer settings. Enter half of your measured kerf (in the example above, 0.08 mm) and LightBurn shifts the cut path outward on outer shapes and inward on holes, so parts come out at their true drawn size. xTool Creative Space and other programs have similar options.

When you do not need kerf compensation

Flat decorative pieces, wall art, ornaments and engraved items need no compensation. Save it for projects where parts slot or press together.

Material thickness matters more than kerf

Our slotted designs are drawn for a specific material thickness, stated in each listing - most often 3 mm (1/8 inch). Plywood sold as 3 mm can measure anywhere from about 2.7 to 3.3 mm, so measure your sheet with calipers before cutting. If it is far from the stated thickness, try a different sheet rather than resizing the file.

Ready to put your settings to work? Browse our box templates and display stands.