What is kerf?

Kerf is the width of material a blade removes as it cuts. The blade doesn't part the material along an infinitely thin line — it grinds away a slot as wide as its cutting edge, and that slot becomes sawdust or swarf. The wider the blade, the more material each cut consumes.

Kerf applies to every cut, not just the first. Slice one length into five pieces and you've made four cuts — four kerfs' worth of material gone, before you even count the pieces themselves.

Kerf depends on the blade and the saw, so treat any figure as a starting point rather than a fact about your setup. As rough guidance:

• Metal-cutting bandsaw — around 1/16 in (about 1.6 mm)
• Standard circular or miter blade — about 1/8 in (3 mm)
• Thin-kerf woodworking blade — closer to 3/32 in (about 2.3 mm)
• Wheel-style tubing cutter — effectively zero, since it displaces material instead of removing it

These are typical ranges, not guarantees. Blade thickness varies between brands and even between blades on the same saw, which is why measuring your own is worth the two minutes it takes.

Make a single cut in scrap and measure the width of the slot it leaves with calipers, or measure straight across the set of the blade's teeth. Either gives you the real number for your machine.

If you'd rather not measure, the blade's packaging or the manufacturer's spec sheet usually lists the kerf. However you find it, the same blade cuts the same kerf every time — so you only need the number once.

Plan as though the blade removes nothing and every stock piece comes up short. Two 24-inch parts don't both fit on a 48-inch board: the cut between them eats a kerf, so you need 48 inches plus that sliver. Across a dozen cuts on one stick, ignored kerf can cost you a whole part — or a whole extra stick.

This is why a good cut optimizer asks for your kerf and subtracts it between every cut. Enter an accurate figure and the layout matches what the saw actually produces; guess low and the plan won't survive contact with the material. NestSolver works this way — set your kerf once and it accounts for it on every cut.