The width of material removed by a cutting tool - the slot left behind after the cut. It includes the tooth set on a saw blade, so it is wider than the blade plate.

The material destroyed by the cuts themselves, as opposed to the offcut. Twenty full-width cuts at 3.2 mm on a standard sheet lose about 2.6% of its area.

What is a typical saw kerf?

About 3.2 mm (1/8") for a full-kerf table saw blade and 2.4 mm (3/32") for a thin-kerf blade. Industrial beam saws run 4-4.8 mm, bandsaws under 1.5 mm.

What kerf should I use on a CNC router?

The cutter diameter. A 6 mm bit has a 6 mm kerf, which is roughly double a table saw and changes layouts noticeably.

How do I measure kerf?

Make ten cuts across a piece of scrap, push the pieces back together, measure how much shorter the reassembled piece is, and divide by ten.

Does kerf really change how many sheets I need?

Only sometimes, and that is the point of checking. It costs nothing when part sizes leave slack, and costs a full row when part sizes divide the sheet almost exactly.

Calculator page · 6 min read

Kerf calculator: how much material your blade eats

Kerf is the width of material a cutting tool destroys as it passes - not the width of the blade body, but the width of the slot left behind. Every cut removes that much, permanently, and on a job with a few hundred cuts it adds up to real sheets and real bars. This page gives typical kerf values by tool, the arithmetic for kerf loss on sheet and linear stock, and the specific situation where a few millimetres costs you an entire part.

Open free sheet cut list optimizer Kerf explained

Kerf loss: the arithmetic

Two formulas cover nearly everything. For a run of identical pieces cut from one length of stock, the stock has to satisfy: (number of pieces × piece length) + (number of cuts × kerf) ≤ stock length. Cutting n pieces from a bar takes n − 1 internal cuts if the last piece finishes at the far end, and n cuts if you trim both ends.

For total area lost on a sheet, multiply the number of cuts by the kerf width by the length of each cut. On a 2440 × 1220 mm sheet, twenty full-width cuts at 3.2 mm kerf destroy 20 × 3.2 × 1220 = 78,080 mm², or about 2.6% of the sheet - before any offcut waste at all.

That 2-3% is the floor. It is not the number that hurts.

When kerf costs you a whole part

Kerf only rounds material away quietly until your part size divides the stock size almost exactly. Then it takes a whole part.

A 2440 mm bar cut into 405 mm pieces looks like six pieces: 2440 ÷ 405 = 6.02. With a 3.2 mm kerf, six pieces need 6 × 405 + 5 × 3.2 = 2446 mm. The bar is 2440 mm. You get five, and the sixth turns up as a shortage halfway through the job.

The same trap on sheets is worse because it compounds in both directions at once. Parts at 610 × 305 mm tile a 2440 × 1220 mm sheet perfectly on paper - four across, four down, sixteen parts. With a 3.2 mm kerf, four across needs 4 × 610 + 3 × 3.2 = 2449.6 mm, and four down needs 4 × 305 + 3 × 3.2 = 1229.6 mm. Neither fits. The grid collapses to three by three: nine parts instead of sixteen. Rotating parts into the leftover strip claws back one or two, but a layout that looked perfect is short by a third.

Close-up of a saw blade showing the kerf slot removed from the workpiece — The kerf is the slot left behind, not the thickness of the blade plate - set teeth make it wider.

Typical kerf widths by tool

Use these as starting points only. Kerf varies with tooth set, blade condition, feed rate, and on thermal processes with power and material thickness. Measuring your own is a five-minute job and worth doing once per machine.

Tool	Typical kerf	Notes
Table saw, full kerf	3.2 mm (1/8")	The default assumption in most cut lists
Table saw, thin kerf	2.4 mm (3/32")	Less strain on underpowered saws
Track saw / circular saw	2.2-3.0 mm	Check the blade, not the tool
Sliding mitre saw	2.4-3.2 mm	Same range as a table saw
Industrial beam saw	4.0-4.8 mm	Thicker plate for stability in a stack
Bandsaw	0.6-1.5 mm	Why resawing wastes so little
Jigsaw	1.5-2.5 mm	Varies with blade and material
CNC router, 6 mm bit	6.0 mm	The bit diameter is the kerf
CNC router, 9.5 mm bit	9.5 mm	Roughly three times a table saw
Fibre laser, sheet metal	0.1-0.4 mm	Widens with material thickness
Plasma	1.5-4.0 mm	Scales with amperage and thickness
Waterjet	0.8-1.2 mm	Slight taper through the cut
Cold saw, metal	2.0-3.0 mm	Blade dependent
Abrasive chop saw	2.5-3.5 mm	Disc wears, so kerf drifts

Thermal processes also leave a heat-affected edge; if your parts are dimension-critical, add finishing allowance separately from kerf.

How to measure your actual kerf

Guessing from the blade packet is usually close enough for wood and usually wrong for anything else. Two methods take five minutes.

Single-cut method: cut a piece of scrap in two, push the halves back together, and measure the total length. The difference from the original is one kerf.
Multi-cut method, more accurate: make ten cuts across a scrap, reassemble, measure the shortfall, and divide by ten. This averages out measurement error.
For a CNC, cut a slot with the bit you will use and measure it with callipers - real bits run under or over nominal.
Re-measure after a blade change or a resharpen; set teeth come back narrower.

Write the number on the machine. It is the single input most likely to be entered from memory and wrong.

Kerf calculator workflow: enter it once, re-run twice

The reason this is a calculator page rather than a formula page is that kerf is not interesting on its own - it is interesting when it changes a sheet count.

Enter your parts and stock in the sheet or linear optimizer, set kerf to your measured value, and run. Then change kerf to zero and run again. The difference in stock count is what kerf costs you on this specific job, in sheets or bars rather than percentages. On most jobs it is zero and you can stop worrying; on jobs where part sizes nearly tile the stock, it is a sheet or two and you have just found it before ordering rather than after.

If the difference is large, that is a design signal as much as a cutting one. Shaving 3 mm off a part dimension sometimes buys back a whole row.

Test kerf on a sheet layout Test kerf on bar stock

Where kerf gets set wrong

Left at zero, which produces layouts that are one part short in reality
Copied from a table saw onto a CNC, where the 6 mm bit removes twice as much
Set to blade plate thickness rather than the set width of the teeth
Applied to a laser or waterjet at wood values, three to thirty times too high
Kept at the old value after switching from full kerf to thin kerf blades
Halved to account for common-line cutting, instead of planning common-line cuts explicitly

Kerf explained in full How kerf affects cabinet cutting

FAQ

What is kerf?: The width of material removed by a cutting tool - the slot left behind after the cut. It includes the tooth set on a saw blade, so it is wider than the blade plate.
What is kerf loss?: The material destroyed by the cuts themselves, as opposed to the offcut. Twenty full-width cuts at 3.2 mm on a standard sheet lose about 2.6% of its area.
What is a typical saw kerf?: About 3.2 mm (1/8") for a full-kerf table saw blade and 2.4 mm (3/32") for a thin-kerf blade. Industrial beam saws run 4-4.8 mm, bandsaws under 1.5 mm.
What kerf should I use on a CNC router?: The cutter diameter. A 6 mm bit has a 6 mm kerf, which is roughly double a table saw and changes layouts noticeably.
How do I measure kerf?: Make ten cuts across a piece of scrap, push the pieces back together, measure how much shorter the reassembled piece is, and divide by ten.
Does kerf really change how many sheets I need?: Only sometimes, and that is the point of checking. It costs nothing when part sizes leave slack, and costs a full row when part sizes divide the sheet almost exactly.