Kerf: Kerf is the width of material removed by a cutting process, such as a laser beam, waterjet stream, plasma arc or saw blade.
Every cut has a width. A fibre laser on thin sheet leaves a kerf of a few tenths of a millimetre; a waterjet leaves one around a millimetre; plasma and saws leave wider ones. The exact value depends on the machine, the nozzle, the material and its thickness. CAM software offsets the cutting path by half the kerf so the part comes out to its drawn size.
What it means for the price
Kerf matters for accuracy and for nesting. Parts in a nest must be spaced at least a kerf apart plus a safety margin, so a wider kerf fits fewer parts on a sheet. Common-line cutting, where neighbouring parts share one cut, saves both material and cut length. In processes such as waterjet, a wider kerf also means more abrasive used per metre.
Example: with a 1 mm kerf and 2 mm of extra spacing, a nest of 50 parts leaves a 3 mm gap between every pair of neighbours, all of it paid for as material. The figures are an example.
Common confusions
Kerf is not taper, the difference in width between the top and bottom of a cut, which grows with thickness on waterjet and plasma. A part that ignores kerf comes out undersized by its full width. Read waterjet vs laser vs plasma.
Go deeper: Waterjet vs laser vs plasma cutting: thickness, accuracy, edge and cost