Discrete ManufacturingFree calculatorPDF, Excel, Word exportLaser Cutting and Fabrication

Laser Cutting Kerf Compensation Calculator (Offset and Programmed Size)

A laser beam removes a strip of material, the kerf, and the finished part is smaller or larger than the programmed line unless the toolpath is offset. This calculator gives the offset per side, the programmed dimension for outside contours and inside features, and how much material the kerf consumes.

Your numbers

Nominal feature size

The finished part dimension on the drawing.

Kerf width

Measured cut width from a test cut at the same material, gas, speed and nozzle.

Feature type

Outside contours are programmed larger by the kerf. Inside features are programmed smaller.

Tolerance (plus or minus)

Material thickness

Total cut length

Sum of all contours cut for the part or the nest.

Material density

Your results

Toolpath offset per side (mm)

0.1

Half the kerf: the beam center runs this far from the finished edge.

Programmed path dimension (mm)

100.2

Center-line dimension: nominal plus kerf for outside, minus kerf for inside.

Error if not compensated (mm)

0.2

Outside parts come out undersize by the kerf. Holes come out oversize by the kerf.

Uncompensated error vs tolerance band

100%

Error as a percent of the total tolerance band. Above 100 percent scraps the part.

Volume removed by kerf (cm3)

1.44

Kerf width times thickness times cut length.

Mass removed by kerf (g)

11.304

Volume times density.

Kerf varies with material, thickness, gas, nozzle, focus position, speed and machine wear, and is not uniform at corners and on small holes. Measure it with a test cut on your machine. Most CAM and laser controllers apply the offset for you.

Save results:

Programmed path dimension vs kerf width

Sweeps Kerf width from 0.05 to 0.6, holding your other inputs fixed.

Nest, cut and scrap data in your ERP

Optional: an expert review of connecting actual cut results and kerf loss to quoting and job costing.

Optional. The tool and every export work without this. No spam.

How to use it

Cut a test shape, such as a 50 mm square with a 20 mm hole, in the same material, gas and nozzle you will use for production. Measure the result with calipers and divide the difference by the number of edges it covers to get the kerf. Enter the nominal feature size, the kerf, and whether the feature is an outside dimension or a hole or slot. The calculator returns the toolpath offset, the programmed center-line dimension and the error you would see without compensation. If you enter the thickness and the cut length you also get the volume and mass lost to kerf.

Measure kerf on your machine, not from a chart
Re-measure after a nozzle change or lens service
Use a separate kerf for each material, thickness and gas
Small holes and tight corners need extra care

How the compensation works

The beam center follows the programmed path and the kerf removes half its width on each side. For an outside contour the path must sit half a kerf outside the finished edge, so the programmed path dimension is the nominal plus the kerf. For a hole or slot the path sits half a kerf inside, so the programmed dimension is the nominal minus the kerf. Controllers and CAM systems do this with a cutter compensation value equal to half the kerf, selecting left or right of the path. Applying it twice, once in CAM and once in the controller, is a classic error.

Worked example

A 3 mm mild steel part on a fiber laser has a measured kerf of 0.20 mm. The nominal outside width is 100 mm with a tolerance of plus or minus 0.1 mm. The offset is 0.10 mm per side and the programmed path dimension is 100.20 mm. A 20 mm hole is programmed at 19.80 mm. Without compensation the part would be 0.20 mm undersize, which is 100 percent of the 0.2 mm tolerance band, so it would sit right on the limit. The kerf also removes about 1.44 cm3 or around 11 g of steel over a 2,400 mm cut length.

Common mistakes

People often enter the offset instead of the full kerf, which halves or doubles the correction. Another is using one kerf for all thicknesses: kerf typically grows with thickness and varies with gas and focus. Small holes cut with high power may taper, with different top and bottom diameters, which a single kerf cannot fix. Last, forgetting that nesting needs spacing at least equal to the kerf plus a safety margin leads to parts that clip each other or lose edge quality.

Frequently Asked Questions

What is a typical kerf for fiber laser cutting?

Roughly 0.1 to 0.5 mm depending on material, thickness, gas, nozzle and focus. Thin sheet cut with nitrogen is at the low end and thick plate at the high end. Always measure on your own machine and material.

Do I offset by the kerf or half the kerf?

Offset each side by half the kerf. The programmed dimension changes by the full kerf, because both sides move. Entering the full kerf into a field that expects the offset doubles the correction.

Is kerf compensation done in CAM or in the controller?

Either, but only one. Most nesting and CAM software writes the offset into the path, and then the controller must have compensation turned off. If both apply it, parts are off by a full kerf.

Why do small holes come out the wrong size?

Heat, taper, piercing and the lead-in strategy affect small holes more than large profiles. Kerf at the top and bottom of the hole differ, and the hole can be bell-shaped. Use test cuts and adjust parameters per hole size rather than relying on one kerf value.

If your cutting jobs, nest programs and material consumption sit in an ERP or shop floor system, Netray can help connect actual cut results and scrap to quotes and costing, using private on-prem tools.

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