Plasma Cut Kerf Loss Calculator
Estimate the kerf offset, material removed and dimensional loss when plasma or laser cutting, so parts come out to size.
How it works
Path offset = kerf ÷ 2 · Material removed = kerf × thickness × cut length · Weight = volume × density · Each cut edge loses one full kerf of size
A plasma or laser torch removes a channel of metal — the kerf — centred on the cut line, so half the kerf disappears from the part and half from the scrap on each side. To hold a dimension you offset the torch path outward by half the kerf on part edges (and inward for holes); miss this and every part comes out undersize by a full kerf across. The tool also totals the metal turned to dross and fume, which matters for nesting yield and for how much of a plate you actually keep.
Worked example
Cutting with a 1.5 mm kerf: offset the path by 0.75 mm per side. Cutting 2000 mm of line in 6 mm mild steel removes 1.5 × 6 × 2000 = 18,000 mm³ = 18 cm³, weighing 18 × 7.85 ÷ 1000 = 0.141 kg. A part cut without offset finishes 1.5 mm undersize on each outer dimension.
Frequently asked questions
Why offset by half the kerf?
The cut is centred on the programmed line, so the kerf straddles it — half into the part, half into the scrap. Offsetting the torch path outward by kerf ÷ 2 puts the finished edge exactly on your dimension.
Does kerf width change with thickness?
Yes. Thicker plate and higher amperage widen the kerf, and the cut is slightly wider at the top than the bottom (bevel). Measure the kerf on a test cut for the exact material and settings you run.
Is plasma kerf the same as saw kerf?
The idea is identical — material lost to the cut — but plasma and laser kerfs are usually narrower and are compensated by a CAM path offset rather than by spacing pieces, since there is no physical blade.
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This calculator is for educational purposes. Double-check important results before acting on them.