What Is Kerf?
Kerf is the width of material a saw blade removes in a single cut. If your blade is 3 mm thick at the teeth, every cut turns a 3 mm strip of board into sawdust. Kerf matters every time you cut several parts from one sheet: ignore it, and the last part comes out short.
Typical kerf widths
| Saw | Typical kerf | Imperial |
|---|---|---|
| Full-kerf table saw blade | 3.2 mm | 1/8 in |
| Thin-kerf table or circular saw blade | 2.2–2.6 mm | 3/32 in |
| Track saw | 2.2–2.8 mm | about 3/32 in |
| Panel saw with scoring blade | 3.2–4.4 mm | 1/8–3/16 in |
| Jigsaw | 1.5–2 mm | 1/16 in |
| CNC router (6 mm bit) | 6 mm | 1/4 in |
The number printed on the blade packaging is the width of the teeth, which is the kerf. If you want to check, cut halfway into a scrap and measure the slot with calipers.
How kerf changes a cut list
Say you need four shelves 300 mm wide from a strip of board 1220 mm wide. Four shelves are 1200 mm, which looks like it fits with 20 mm to spare. But three cuts between four shelves with a 3.2 mm kerf remove almost 10 mm, and if you also trim 10 mm from the factory edge, there is nothing left over. With a 4 mm panel-saw blade, the fourth shelf is short.
That is why a good cut list optimizer asks for the kerf: it leaves one kerf between every pair of neighbouring parts on the sheet, so every part keeps its exact size.
Cut on the waste side of the line
Kerf is also the most common reason parts come out a few millimetres short. When you mark a cut, the line is the edge of the part. Put the blade on the waste side of the line so the kerf comes out of the offcut, not out of your part. On a table saw, measure from the fence to the tooth that leans toward the fence.
Kerf and edge trim
Factory edges of MDF, melamine and plywood are often damaged or not perfectly square. Most workshops trim 5–10 mm from each edge before cutting parts. In the optimizer this is the edge trim setting, separate from the kerf.
Kerf bending
“Kerf bending” is a different use of the word: you cut a series of parallel kerfs part-way through a board so it can bend into a curve. The closer and deeper the kerfs, the tighter the bend. Flexible MDF and plywood do the same job without cutting.
Should I set the kerf a little larger?
A little, yes. Blades wobble slightly and cuts are never perfectly straight. Many carpenters enter 4 mm for a 3.2 mm blade so the layout leaves a safe margin. The cost is a few millimetres per sheet; the benefit is no surprise at the end of the sheet.
Frequently asked questions
What does kerf mean?
Kerf is the slot a saw blade leaves in the material: the width of wood turned into sawdust by one cut.
How wide is a typical saw kerf?
A full-kerf table saw blade cuts about 3.2 mm (1/8 in), a thin-kerf blade about 2.4 mm (3/32 in), track saws 2.2–2.8 mm and panel saws 3.2–4.4 mm.
Do I add kerf to each part?
No. Each part keeps its exact size; the kerf is the gap between parts on the sheet. The optimizer leaves one kerf between neighbouring parts.
Why are my parts too short?
Usually because the cut was made on the wrong side of the line, so the kerf came out of the part instead of the waste.