What the saw kerf is
The kerf is the width of material a blade removes on each pass. The teeth do not slice a zero-width line; they grind a slot and turn that strip into sawdust. For most circular saw and table saw blades the kerf is about 1/8 in (around 3 mm). Thin-kerf blades remove a little less, and a jigsaw or track saw blade may differ, so the number is yours to measure rather than assume.
That width matters because a cut list assumes you can lay parts edge to edge. In reality, between any two parts sits one full kerf of lost material. One cut is easy to shrug off. The trouble starts when you make a lot of them.
Why the kerf adds up, with a worked example
Each cut eats one kerf, so the loss is cumulative across a row of parts. Make ten cuts at 1/8 in and you have removed more than a full inch (10 multiplied by 1/8 in is 1.25 in). On a metric sheet, ten cuts at 3 mm remove 30 mm. That is real material, gone before you have placed your last part.
Take a worked example. You want to cut six shelves, each 15 in wide, from one 96 in length of an 8 ft sheet. The bare math says 6 multiplied by 15 in is 90 in, which fits inside 96 in with room to spare. But each shelf sits behind a cut line. Six cuts at 1/8 in remove 6 multiplied by 0.125 in, which is 0.75 in. So you really need 90 in plus 0.75 in, which is 90.75 in. Still inside 96 in, but the cushion just shrank from 6 in to a bit over 5 in.
Now push it: ask for seven shelves at 15 in. Bare math is 105 in, already past 96 in, so you knew a second length was needed. The point is subtler on tight layouts. When parts nearly fill a sheet, a forgotten kerf is exactly what tips the final part off the panel and forces you to buy an extra sheet you did not budget for.
How to measure your blade's kerf
Do not guess from the box. Measure across the carbide teeth with a caliper, since the teeth are set slightly wider than the steel body and they decide the slot width. No caliper handy? Make one test cut in scrap, then measure the width of the slot. Write that number down (for example 0.125 in or 3.2 mm) and reuse it, because the same blade gives the same kerf every time.
How a cut list calculator handles the kerf
A cut list calculator removes the arithmetic. You enter the kerf once, and the optimizer subtracts one kerf for every cut line as it packs parts onto the sheet, adding the losses cumulatively rather than once. The result is a layout where each part is sized for its true finished dimension, the cut sequence already allows for the lost strips, and the sheet count reflects what you will actually use at the saw.
This is the difference between a plan that looks right on paper and one that comes out right on the bench. cutlistlab does it for you: set the kerf, enter your parts, and the cutting plan, the cut list, and the number of sheets all account for the blade. For the background on blades and why thin-kerf matters, see the guide on saw kerf explained.
Stop counting blade widths by hand. Open the free calculator, enter your kerf and your parts, and get a cutting plan that already has the kerf built in. No sign-up, nothing to install.
Frequently asked questions
What is the saw kerf?
It is the width of material the blade turns into sawdust on each cut, often about 1/8 in (around 3 mm). Thinner blades remove less.
How do I measure my blade's kerf?
Measure across the carbide teeth with calipers, or make a test cut and measure the slot. Enter that figure as your kerf.
Why does the kerf add up across many cuts?
Each cut removes one kerf, so it is cumulative. Ten cuts at 1/8 in remove over an inch, enough to push the last part off a full sheet.
How does the calculator handle kerf?
You set it once. The calculator subtracts one kerf per cut line cumulatively, so every part is cut to its true size and the sheet count is realistic.