Saw Kerf Explained: Why Your Cuts Come Up Short
You measured twice. You cut once. And the last piece is still 3/8" too short. Nothing is wrong with your tape or your technique — the missing wood is on the floor, as dust. Kerf is the width of material the blade destroys on every cut, and if your cut list doesn't account for it, the list is fiction.
What kerf is
A saw blade isn't a line — it's a body with width. The teeth are wider than the plate so the blade doesn't bind, and the slot they leave is the kerf. Cut a 96" board exactly in half and you don't get two 48" pieces; you get two pieces of about 47 15/16", because the blade ate the other 1/8".
How wide common blades cut
| Blade / tool | Typical kerf | In millimetres |
|---|---|---|
| Full-kerf table saw blade | 1/8" | 3.2 mm |
| Thin-kerf table saw blade | 3/32" | 2.4 mm |
| Circular saw (framing blade) | ~1/8" – 5/32" | 3.2 – 4 mm |
| Track saw blade | ~3/32" – 1/8" | 2.2 – 2.8 mm |
| Jigsaw blade | ~1/16" – 3/32" | 1.5 – 2.4 mm |
| CNC router (1/4" bit) | 1/4" | 6.35 mm |
Note the CNC row: a router bit's "kerf" is its full diameter, double a table saw blade. Layouts headed for a CNC need a bigger allowance, not a smaller one — relevant if you export DXF cutting layouts.
How the error compounds
One kerf is trivia. Eight of them is a missing part. Say you want eight 11 7/8" pieces from a 96" board. Area math: 8 × 11 7/8" = 95" — fits with an inch to spare. Reality: seven cuts between the eight pieces eat 7 × 1/8" = 7/8". Total consumed: 95 7/8" out of 96". You'll get your eight pieces with 1/8" to spare — but only if every cut is perfect. Wanted eight 12" pieces instead? 96" + 7/8" of kerf = 96 7/8". The eighth piece does not exist, no matter how carefully you cut.
Sheet goods are worse, because cuts happen in two directions and a big layout has twenty or thirty of them. This is one of the main reasons naive estimates undercount — see how many sheets of plywood do I need?
Accounting for kerf without going mad
By hand, the rule is: sum of part lengths + (number of cuts × kerf) must fit the stock. That's manageable for one board and miserable for a cabinet's worth of plywood. The practical answer is to let software carry the arithmetic:
Two habits to pair with it: set the kerf to your measured value rather than the default, and when a layout "just barely fits," treat that as a warning — one wandering cut and the last part is scrap. Give yourself a part you can afford to lose, or nudge a dimension. More waste-trimming tactics: how to reduce plywood waste.
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Get Lifetime Access →Saw kerf — Frequently Asked Questions
What is saw kerf?
The width of material the blade removes on each cut. A standard table saw blade takes about 1/8" (3.2mm); thin-kerf blades about 3/32" (2.4mm).
How do I measure my saw's kerf?
Cut into scrap and measure the slot with calipers, or read the tooth width stamped on the blade. Use the measured value — worn blades cut wider.
Does kerf matter for a cut list?
Decisively. The error compounds with every cut — after eight cuts you're an inch off, which is the difference between getting the last part and not.
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