Laser kerf & tolerance calculator
The beam has width, so parts cut smaller and holes cut larger than drawn. Enter your nominal size and kerf to get the exact dimensions to draw for snug box joints, inlays and press fits.
- Measure your real kerf in 30 seconds. Cut a 20 mm square, measure it with calipers — say it comes out 19.85 mm. Kerf = 20 − 19.85 = 0.15 mm. That's your number; every preset here is just a starting guess.
- Kerf changes with material and power. Thicker stock and higher power widen the kerf. Re-measure when you switch from 3 mm to 6 mm ply, or acrylic to wood.
- Finger joints need kerf on both parts. A tab is an outer edge (comes out smaller) and its slot is a hole (comes out bigger) — apply kerf to both or the joint ends up loose by a full kerf.
- Start tight, sand loose. For press fits aim for a snug 0.05–0.1 mm interference; you can always sand a joint looser, but you can't add material back.
What kerf is and why it matters
The laser beam has width, so it burns away a thin channel — the kerf — centred on your cut line. That means a part cut on its outline comes out slightly smaller than drawn, and a hole comes out slightly larger. For decorative work you'll never notice; for boxes, gears, inlays and press-fit joints, half a kerf on each side is the difference between snug and sloppy.
Outer edge / tab → draw at nominal + kerf. Hole / slot → draw at nominal − kerf. Then add a little clearance for a slip fit, or remove a little for a press fit.
Typical kerf: CO2 on acrylic ~0.15 mm, CO2 on wood ~0.2 mm, diode ~0.1 mm, fiber ~0.08 mm — but these vary with power, speed and thickness, so measure your own (see the tips above).
FAQ
What is laser kerf?
Kerf is the width of material the laser beam vaporises as it cuts — the thin channel centred on your cut line. Because of it, a part cut on its outline finishes about one kerf smaller than drawn, and a hole finishes about one kerf larger. Typical kerf is 0.1–0.2 mm on a CO2 laser.
How do I compensate for kerf?
Draw outer edges and tabs at your target size plus the kerf, and draw holes and slots at the target size minus the kerf. For fitted parts, add a small clearance (0.05–0.15 mm) for a slip fit or subtract a little for a press fit. This calculator gives you both adjusted dimensions from your nominal size.
How do I measure my laser's kerf?
Cut a square of a known size — say 20 mm — and measure the actual part with calipers. The difference is your kerf: if a 20 mm square comes out 19.85 mm, your kerf is 0.15 mm. Re-measure when you change material or thickness, since kerf grows with power and stock thickness.