Saw Kerf Calculator
Account for the material your blade turns into dust. Work out how much length a series of cuts removes, or the shortest board that will actually yield the pieces you need — including the kerf between them.
Calculator
Measure your own — a reground blade cuts wider than its label.
This is worth one kerf per board — often the difference between the last piece fitting and not.
Result
Minimum stock length
2,419.2 mm
6 pieces + 6 cuts of kerf
- This board is 19.2 mm short of the minimum. You need a longer board or one fewer piece.
Kerf loss depends on your blade and on how many cuts you actually make, which depends on your cutting sequence. This calculator makes the cut count explicit rather than assuming one; check that the assumption shown matches how you plan to break the board down.
Why kerf matters more than it looks
A saw does not divide a board, it removes a slot. That slot — the kerf — is typically 3.2 mm on a full-kerf table saw blade, 2.4 mm on a thin-kerf, around 2.2 mm on a track saw and about 1 mm on a bandsaw.
Three millimetres sounds negligible until you multiply. Cutting ten pieces from one board removes around 30 mm, which is more than most people leave as slack. It is precisely why the last piece off a board so often comes up short: the arithmetic was done on the finished lengths and the blade was never included.
The effect compounds with the number of parts, not the length of them. A board cut into twenty short pieces loses twice as much to the blade as one cut into ten long ones, even though the finished total is identical.
The cut-count question, stated openly
Cutting four pieces from one board takes either three cuts or four, and which one applies is a genuine choice rather than a fact of arithmetic.
If the board already has a usable square end and the last piece runs out to the far end, three cuts separate four pieces. If you need to trim the first end square, or the final piece needs its own clean-up cut, you make four.
That difference is exactly one kerf per board — around 3 mm. Small, but it is the difference between the last piece fitting and not. Rather than pick one silently, this calculator asks which applies, and the loss-mode lets you state the cut count outright when you already know it.
Worked example
You need six rails at 400 mm from one length of stock, cutting with a full-kerf blade at 3.2 mm, and you will trim the leading end square first.
Finished material: 6 × 400 = 2400 mm. Cuts: six, since every piece including the last gets its own cut. Kerf allowance: 6 × 3.2 = 19.2 mm. Minimum stock: 2400 + 19.2 = 2419.2 mm.
A 2400 mm board is therefore 19.2 mm short — it looks like an exact fit and is not. You need a 2500 mm board, or five rails from this one and the sixth from elsewhere.
Measuring your actual kerf
Blade specifications are nominal and the real kerf differs: the plate can wobble slightly, carbide teeth get reground narrower over their life, and a blade with any run-out cuts wider than its teeth measure.
To measure it, crosscut a piece of scrap, then measure the two offcuts and the original together — the difference is one kerf. Or make a single cut partway into a board and measure the slot directly with calipers.
Use your measured figure rather than the packaging. On a project with many parts a 0.4 mm discrepancy across thirty cuts is 12 mm, which is enough to lose a part.
Common mistakes
Planning a cut list from finished dimensions alone, with no kerf allowance anywhere, is the standard version. It works until the last piece.
Assuming kerf applies once per piece regardless of layout is a subtler one. It depends on the sequence — which is why the cut count is a stated input here rather than something derived behind your back.
Using nominal blade kerf on a well-used blade is the third, and it always errs in the same direction: a reground blade cuts a wider slot than its label claims, never a narrower one.
Apply kerf to an entire project
Doing this by hand for every part is where cut lists go wrong. Plank CAD works kerf and joinery allowances into the part dimensions across the whole design — currently for bookcases and open storage cabinets.
Common questions
A full-kerf table saw blade cuts about 3.2 mm (1/8"), a thin-kerf blade about 2.4 mm (3/32"), a track saw around 2.2 mm and a bandsaw roughly 1 mm depending on the blade. Measure your own rather than trusting the packaging, since a reground blade cuts wider than its stated width.
Five if the board has a usable square end and the last piece runs out to the far end. Six if you trim the leading end first or the final piece needs its own cut. That single extra cut is one kerf of material, which is often exactly the amount that decides whether the last piece fits.
Over many cuts, yes. Switching from 3.2 mm to 2.4 mm saves 0.8 mm per cut — 24 mm over thirty cuts, which is most of a part on a small project. Thin-kerf blades also demand less of an underpowered saw, though they can deflect more in thick hardwood.
Not to the parts — the parts keep their finished dimensions. Kerf is added to the stock you cut them from, once per cut. That is why a cut list and a stock list are different documents, and why breaking a sheet or board down needs a layout rather than a per-part allowance.