What Is Kerf Allowance and Why It Matters for Accurate Cuts

Miss kerf allowance once and your parts come out 3 mm too big — every time. Or worse, you run out of stock on the last sheet because the optimizer didn’t know your blade eats 3.2 mm per cut. Kerf is the most overlooked input in cutting optimization, and it takes about thirty seconds to set correctly. Here’s everything you need to know.

What Is Kerf?

Kerf is the width of material removed by a cutting tool in a single pass. When a saw blade cuts through a board, the teeth don’t split the wood cleanly at a line — they grind away a strip of material equal to the blade’s tooth set width. That strip becomes sawdust.

A standard table saw blade has a kerf of about 3.2 mm (1/8 in). A thin-kerf blade runs around 2.4 mm. A CNC router bit might remove 3 mm to 6 mm depending on the bit diameter. A laser cutter’s kerf is as narrow as 0.2 mm.

The key point: kerf is real material that vanishes. After every cut, your remaining stock is shorter by the kerf width. Ignore it and your math is wrong from the first cut.

What Is Kerf Allowance?

Kerf allowance is the practice of adding the kerf width to the space between adjacent parts in your cut plan. Without it, the optimizer assumes cuts happen at an infinitely thin line — which no physical tool can do.

Here’s what happens in practice. Say you have a 1000 mm board and need two 500 mm parts. Without kerf allowance, the optimizer says: 500 + 500 = 1000 mm. Perfect fit, zero waste. But your saw blade removes 3.2 mm. After the first cut you have a 500 mm piece and a 496.8 mm piece. The second part is too short.

With 3.2 mm kerf allowance, the optimizer calculates: 500 + 3.2 + 500 = 1003.2 mm required. It knows the board is only 1000 mm, so it either flags the problem or arranges parts differently.

In 2D panel cutting, kerf allowance works the same way — it adds a gap between every adjacent part on the sheet. For a standard 4×8 ft panel (1220×2440 mm) with 3.2 mm kerf, the usable area shrinks slightly with every internal cut. On a sheet with 15 cuts, that’s nearly 50 mm of material turned to dust.

Typical Kerf Values by Tool

How to Set Kerf Allowance in CutOptim

In CutOptim, kerf is a dedicated input field on the optimization screen — not buried in settings. Before you run the optimizer:

1. Find the Kerf field (labeled in millimeters by default).
2. Enter your blade’s kerf width. If you’re unsure, make a test cut in scrap material and measure the slot width with calipers.
3. Run the optimization. CutOptim automatically adds the kerf gap between every adjacent part in the layout.

That’s it. The optimizer handles the rest — adjusting part positions, recalculating yield, and accounting for kerf on every internal cut. If you change blades or switch to a CNC router, update the kerf value and re-run.

What Happens If You Forget Kerf Allowance?

The error compounds with every cut. Here’s a concrete example:

You’re cutting 10 shelves from a sheet of 18 mm melamine-faced MDF. Each shelf is 400 mm wide. Without kerf, the optimizer says you need 4000 mm of stock width (10 × 400 mm). A 4×8 ft panel is 1220 mm wide, so that’s about 3.3 sheets — let’s say 4 sheets with the length dimension considered.

Now add kerf. With 9 internal cuts at 3.2 mm each, kerf consumes 28.8 mm — nearly 30 mm of extra width. That’s like adding a phantom 11th shelf. The optimizer that ignored kerf will try to fit parts that physically don’t fit, and your last piece will be 28.8 mm too short.

On bigger jobs the effect is worse. A 40-part cabinet project with 3.2 mm kerf can accumulate over 120 mm of unaccounted material loss. That’s an extra half-sheet of plywood you didn’t buy.

The fix is trivial: enter kerf once, and the optimizer does the math on every cut. There’s no reason to skip it.