What is laser kerf?

ForEducators · Students

Updated 1 October 2026 Sources checked · Not externally reviewed

Short answer

Kerf is the width of material removed by a cut. Because the beam removes a narrow strip of material, a part cut on a programmed line will not come out exactly the size of the drawing. An outside piece tends to be slightly smaller, and an opening tends to be slightly larger, unless the design or software compensates.

The same tab-and-slot joint cut without and with a kerf allowance Two top views of a tab sitting in a slot cut in a sheet, both drawn to the same nominal size shown as a dashed outline. On the left, with no allowance in the file, the finished slot comes out wider than the dashed outline and the finished tab comes out narrower, leaving a visible gap on both sides, so the joint is loose. On the right, with an allowance based on the measured kerf applied in the file, the slot and tab land close to the nominal size and only a tiny gap remains, so the joint is snug. Gaps are exaggerated and no measurements are given. No allowance in the file comes out loose slot grows, tab shrinks Allowance applied in the file comes out snug file offset by the measured kerf size drawn (same in both) size that comes out Same drawing, same nominal size. Only the allowance differs.
Exaggerated for legibility, and carrying no numbers. Kerf makes openings larger and outside pieces smaller, so a joint drawn to one nominal size comes out loose unless the file compensates. There is no universal kerf value, so cut a coupon from the same sheet, measure it, and use that result.

There is no dependable universal kerf value. It changes with the material and its thickness, focus, and the machine and settings used. For fitted parts, students should cut a small coupon from the same sheet, measure the result with an appropriate tool, record the conditions, and use that measured width in the design; compensation offsets each edge by half of it.

Sources

  1. LightBurn Software (laser control software documentation)Kerf – What it is and How to Compensate (LightBurn 2.2 User Guide)Defines kerf as the gap the beam removes, explains why uncompensated parts come out undersized and openings oversized, and notes that kerf varies with material, thickness, speed and power. Software documentation, not a machine specification. Link checked September 2026.
  2. Harvard Graduate School of Design Fabrication Lab (academic laser-cutter training documentation)Laser Training ChecklistOne university fab lab's training checklist: kerf can vary between machines, settings and materials, so cut a test part and measure it against the drawing. Link checked September 2026.
  3. Rayforge (open-source laser control software documentation)Kerf CompensationTreats kerf as the full width removed and shows compensation moving each edge by half of it, with a worked example; also names focus and cut settings among what changes kerf. Software documentation from one open-source project. Link checked September 2026.

Sources are checked by Laser TeamWork, not by an outside expert. General guidance: your machine’s manual and your school’s procedures come first. Report a correction.

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