What is kerf on a saw blade and how do you account for it

What kerf is

Kerf is the slot a saw leaves behind: the width of wood the blade turns into sawdust on each pass. WoodGearLab's explainer notes that on most modern carbide-tipped blades the kerf is set by the widest part of the teeth, the carbide tips, not by the thickness of the steel plate. Diablo's specifications show the gap in numbers: its D0724A 7-1/4 inch circular saw blade has a .040 inch plate and a .059 inch kerf.

That tooth width is why the riving knife has to sit between two limits. WoodGearLab's rule is that the knife must be thinner than the kerf and thicker than the blade plate, so switching between full-kerf and thin-kerf blades can mean switching knives as well.

Kerf is also why pieces cut from a board never add back up to the board. Each cut spends a strip of material, and on a sheet that is cut many times the total grows. TableSawGuide's example: ten cuts with a 1/8 inch full-kerf blade remove 1.25 inches of material.

How wide common blades cut

Full-kerf 10 inch table saw blades cut about 1/8 inch, or 0.125 inch, according to both WoodGearLab and TableSawGuide. Freud's LM72R010 heavy-duty rip blade, for example, is listed at .126 inch.

Thin-kerf blades cut about 3/32 inch. TableSawGuide puts them at about 0.091 inch and WoodGearLab at about 0.094, and Freud's LU86R010 thin-kerf general purpose blade is listed at .094. WoodGearLab estimates that a full-kerf blade removes about 33 percent more material than a thin-kerf one, and suggests thin-kerf blades for lower-powered 120V saws and full-kerf blades where a higher-powered cabinet saw can use their stability.

Other saws differ. Festool lists a cutting width of 2.2 mm, or 3/32 inch, for its 160 mm TS 55 track saw blades, Diablo lists .059 inch for several of its 7-1/4 inch circular saw blades, and TableSawGuide notes that a dado stack cuts a quarter inch or wider. The only number that matters for your layout is the one your blade actually cuts, and TableSawGuide's advice is to measure your own blade, since kerf varies slightly by tooth grind and brand.

Where the kerf goes when you measure

Every cut has a keeper side and a waste side. Woodsmith's track saw advice is to align the guide so the kerf falls on the waste side of the cut. If the blade splits your pencil line instead, the part loses half a kerf, and if two parts share that line, both come out short.

On a table saw, the distance you set between the fence and the blade is the width of the piece against the fence, and the kerf comes out of the other piece. When you rip several parts from one panel, measure each new rip from the freshly cut edge rather than calculating it from the panel's original width.

When you plan on paper, add one kerf for every cut between two parts. TableSawGuide gives the same rule: add the kerf between each part when planning, because every cut consumes its kerf width.

Worked examples on a 4 by 8 sheet

Crosscutting a 96 inch length into four 24 inch parts takes three cuts. With a 1/8 inch kerf those cuts use 3/8 inch, so three parts come out at 24 inches and the last at 23 5/8. With a 3/32 inch thin-kerf blade the last part is 23 23/32 inches, still short.

Ripping a 48 inch width into strips works the same way. Two 16 inch strips and two 1/8 inch cuts leave 15 3/4 inches for the third. If you need three full 16 inch strips, plan those parts across more than one sheet. Trimming a factory edge first costs one more kerf plus whatever you take off.

In millimeters the arithmetic is the same. A 2.2 mm track saw kerf over ten cuts removes 22 mm, a little under an inch.

SawNest, a cut list app for sheet goods, asks for your blade's kerf when you set up a project and subtracts it from every cut in the layout. It takes inches with 1/16 fractions or millimeters, so the numbers you type match the tape measure.

Common kerf mistakes

Planning with one blade and cutting with another. A layout drawn for a 1/8 inch kerf and cut with a 3/32 inch blade, or the other way round, no longer adds up, and the last part on each strip comes out a different size than planned. Update the kerf whenever you change blades.

Measuring the plate instead of the teeth. The plate is thinner than the cut. Because the carbide tips set the kerf, measure the slot the blade leaves in scrap, not the steel.

Splitting the line. Cutting down the middle of a shared line takes half a kerf from each part. Mark which side is waste before you cut.

Leaving the trim cut out of the plan. Squaring up a factory edge is a cut like any other. It costs a kerf plus the strip you remove, and on a tight layout that can decide whether the last part fits.

Frequently asked questions