Saw kerf is the width of material a blade removes as it cuts — the thin slice of waste turned into chips or dust on every single cut. It isn't zero, and on real jobs it isn't negligible: ignore it in a cutting list and the plan will call for more material than the stock you actually have.
Why kerf isn't zero
A blade doesn't split material along an infinitely thin line. The teeth are set slightly wider than the blade's body so the cut clears without binding, and that set — plus any wobble in the cut — removes a real strip of material. Typical circular saw blades remove somewhere in the range of 2–4mm per cut; band saws and thin-kerf blades can be narrower, and abrasive or thicker blades wider. There's no universal number — the right kerf value is whatever your specific saw and blade actually remove, measured on your own equipment.
Why it matters for a cutting list
Say you need two 1000mm pieces from a single stock length. On paper, 2000mm of stock is exactly enough. In practice it isn't — the saw removes a few millimetres between the two pieces, so a stock length of exactly 2000mm comes up short. The kerf has to be added back for every cut on the bar, not just accounted for once.
This compounds fast. A bar cut into 8 pieces loses kerf on (typically) 7 or 8 cuts depending on whether the trailing cut off the bar's own end counts (see "trailing cut kerf" below) — at 4mm kerf, that's 28–32mm of material gone before a single piece is measured out. On a job with dozens of bars, that adds up to real, avoidable shortfall if it isn't in the plan from the start.
Trailing cut kerf
Some shops count kerf on every cut needed to free a piece from the bar, including the very last one; others don't charge kerf on a cut that falls exactly at the bar's own end (nothing is lost past the end of the material). Barcut Pro's engine supports both conventions — this is what the "trailing cut kerf" setting controls — so the plan matches how your saw and your shop actually account for the last cut on a bar, not a generic assumption.
Kerf vs. end trim — two different losses
Kerf and end trim are often confused but they're not the same thing:
- Kerf is lost between cuts, once per cut, proportional to how many cuts a bar has.
- End trim is a fixed calibration offset removed from both ends of every bar regardless of how it's cut — common on machines that need a clean, squared reference edge before the first real cut.
A cutting list that only accounts for one of these will still be wrong, just in a different way. Barcut Pro's optimizer takes both as separate inputs for exactly this reason.
A real example
Using Barcut Pro's own optimizer on a mixed cutting list — 2400mm × 4, 1840mm × 3, 1210mm × 5, with 6200/5600/4500mm stock available, 5mm kerf and 15mm end trim per side — the engine returns a 4-bar plan:
| Stock length | Cuts |
|---|---|
| 6200mm | 2400 + 1210 + 1210 + 1210 |
| 6200mm | 1840 + 1840 + 1210 + 1210 |
| 5600mm | 2400 + 2400 |
| 4500mm | 2400 + 1840 |
Every one of those bars has kerf deducted at each internal cut and end trim taken off both ends before anything else is measured — the plan above is what's actually achievable at the saw, not an idealized version that would come up short once the blade starts cutting.
Getting your own kerf number
Measure it directly rather than guessing: cut two same-length test pieces from a longer piece of your actual stock, on your actual saw, with your actual blade. Measure the two resulting pieces and compare their combined length to the original — the difference is your real kerf. It'll vary by blade condition, material, and machine, so re-check it periodically rather than assuming a number that worked a year ago still applies.
Once you know your saw's real kerf, try the free 1D cutting optimizer — enter your cutting list, your stock lengths, and your measured kerf, and get a plan that accounts for it on every cut.