Short answer: Laser kerf in acrylic is typically about 0.006 to 0.010 in. (0.15 to 0.25 mm) on a well-focused CO2 laser. That's a little wider than the focused beam, which is about 0.004 to 0.007 in. with a standard 2 in. lens. Kerf grows with sheet thickness, slower or hotter cuts, and poor focus. To compensate, offset each cut path by half the kerf: outward on outside edges, inward on holes and slots. For tight fits, cut a test comb first.

Key facts

  • Typical kerf, 1/8 to 1/4 in. acrylic: about 0.006 to 0.010 in. (0.15 to 0.25 mm) total.
  • Offset per side: half the kerf, about 0.003 to 0.005 in. (0.08 to 0.13 mm).
  • Focused spot size: 0.004 to 0.007 in. with a 2 in. focal-length lens; 0.003 to 0.0065 in. with a 1.5 in. lens (Epilog).
  • Untuned cuts can be much wider: a 2023 lab study on 3 mm acrylic with a 50 W tube laser measured cut widths of 0.51 to 1.32 mm (0.020 to 0.052 in.). Slow speeds gave the widest cuts.
  • Taper: the cut is slightly wider at the top than at the bottom. You'll notice it on 3/8 and 1/2 in. sheet.
  • Bigger variable for slots: actual sheet thickness, which often differs from nominal by more than the kerf.

What is kerf?

Kerf is the width of the cut. A saw blade's kerf is the thickness of its teeth. A laser's kerf is the width of the channel the beam vaporizes and melts. Draw a 2.000 in. square, and if the laser follows the line exactly, half the kerf comes off each side. The part measures a little under 2 in., and the hole it leaves in the sheet measures a little over.

How wide is laser kerf in acrylic?

On a well-tuned CO2 laser cutting 1/8 to 1/4 in. sheet, the kerf is typically about 0.006 to 0.010 in. (0.15 to 0.25 mm). The floor is set by the optics. Epilog gives its standard 2 in. lens a focused spot of 0.004 to 0.007 in., and acrylic melts back slightly from the beam, so the cut ends up a little wider than the spot.

Kerf isn't one fixed number, though. Published lab tests show how far it can move. A 2023 study in MethodsX cut 3 mm acrylic on a 50 W glass-tube laser and measured cut widths from 0.51 to 1.32 mm, with slower speeds giving wider cuts. Those settings weren't tuned for narrow kerf, but they show what drives it:

  • Thickness. Thicker sheet needs more energy, a longer dwell, and often a longer lens, so the cut widens. Expect the low end of the range on 1/8 in. and the upper end on 3/8 and 1/2 in.
  • Focus and optics. The beam is narrowest at its focal point and wider above and below it. A 1.5 in. lens gives a smaller spot. A 4 in. lens gives a straighter but wider cut on thick sheet.
  • Power and speed. Slower, hotter cuts melt more material from the walls.
  • Material. Cast and extruded acrylic, and different colors, melt a little differently.

Treat any kerf figure as a typical value, not a guarantee. Add typical laser tolerance of about ±0.005 in., and the fit you can count on without testing is a few thousandths of an inch.

What is kerf taper?

The focused beam spreads above and below its focal point, so the cut is slightly V-shaped: wider at the top, narrower at the bottom. On 1/8 and 1/4 in. sheet the taper is small enough to ignore for most work. On 3/8 and 1/2 in. it shows up in tight joints. A slot will be a touch wider on the top face than on the bottom face, and a part's bottom face will be a touch larger than its top.

Laser makers fight taper on thick sheet by focusing partway into the material. Trotec suggests about one-third of the thickness for sheet over 1/4 in., plus longer lenses. If taper matters, tell us which face is critical. For truly square edges on thick parts, routing is the better process (laser vs router edges).

How do you compensate for kerf?

Offset your cut paths by half the kerf, so the edge of the beam, not its center, lands on your intended line:

  1. Outside profiles (the outline of a part): offset outward by half the kerf, about 0.003 to 0.005 in.
  2. Inside cutouts (holes, slots, windows): offset inward by half the kerf.
  3. Check the result: a 1.000 in. test square should measure 1.000 in. If it measures 0.992 in., your full kerf is 0.008 in.

Most CAD programs have an offset command: Object > Path > Offset Path in Adobe Illustrator, Path > Outset/Inset or Dynamic Offset in Inkscape, Offset in Fusion and AutoCAD. Parametric CAD lets you set kerf as a variable so you can change it later. Inkscape's default Outset step is set in preferences (Steps > Inset/Outset by), so set it to your half-kerf value before using it.

Tip: for most orders, don't compensate yourself. Draw the part at its finished size and we'll account for kerf. If you've already offset your paths, say so in the order notes so it isn't applied twice.

Kerf and slots: the bigger problem is sheet thickness

For tab-and-slot parts, kerf is only half the story. Sheet sold as 1/4 in. usually measures around 0.22 to 0.24 in. and varies across the sheet (actual acrylic thickness). That variation is often bigger than the kerf. Design slots from the measured thickness, then adjust for kerf. More in tab and slot design for acrylic.

Use a test comb

When a fit really matters, cut a test comb first. Make it a strip with a row of slots in small steps, for example from 0.005 in. under the measured sheet thickness to 0.010 in. over, in steps of 0.002 in. Label each slot with a small engraved number. Try a scrap of the same sheet in each slot and pick the one that fits the way you want. It's the fastest way to take kerf, taper, and thickness out of the guesswork, and it costs very little next to a full run of parts that don't fit.

Press fits and kerf

A press fit needs a small interference, usually only a few thousandths of an inch. That's about the same size as the kerf variation, which makes press fits in acrylic hard to hit consistently. The hoop stress can also crack the part later, especially along a laser-cut edge, which already carries some stress. Read press-fit tolerances in acrylic before you design one.

Ready to cut? Upload your drawing and mention any parts that fit together.

Questions

What is laser kerf in mm for 3 mm acrylic?

Typically about 0.15 to 0.2 mm on a well-focused CO2 laser, so offset each side by about 0.08 to 0.1 mm. Badly focused or very slow cuts can run 0.5 mm or more, so test if your fit depends on it.

How do I measure my laser's kerf?

Cut a 1.000 in. (or 25 mm) square, measure it with calipers, and subtract the measurement from the drawn size. The difference is the full kerf, and half of it is your offset per side. Measure both the top and bottom faces if taper matters.

How do I make an acrylic inlay fit with no gap?

Cut the pocket and the inlay from the same drawing, and offset the inlay outward and the pocket inward by half the kerf each. Cut a test pair first, since a zero-gap fit is very sensitive to small variations.

Does routing have kerf too?

Yes. It's the diameter of the bit, often 1/8 to 1/4 in. CNC software offsets for it automatically, so you just draw the finished part.

Sources