Typical kerf widths
| Blade | Kerf | Millimetres |
|---|---|---|
| Full-kerf 10 in table saw blade | About 1/8 in (0.125 in) | About 3.2 mm |
| Thin-kerf 10 in table saw blade | About 3/32 in (0.094 in) | About 2.4 mm |
| Track saw blade | About 1/16 to 3/32 in | About 1.7 to 2.2 mm |
| Circular saw blade | Varies by blade | Read the packaging |
Thin-kerf blades remove about a quarter less material, which helps lower-powered saws. Full-kerf blades are stiffer and less prone to deflect. If your table saw has a riving knife, make sure it is no thicker than the blade's kerf, or the board will bind on it.
Measure your real kerf
The number on the package is a starting point. Teeth wear, blades wobble a little, and some cut slightly wider than spec. Make a short cut into a scrap of the same material, then measure the slot with calipers or a set of feeler gauges. Use that number in your plan.
Why the last part doesn't fit
Say you want four 12 in wide strips from a 48 in wide sheet. On paper 4 × 12 = 48, a perfect fit. At the saw you make three cuts, and each removes 1/8 in: 3 × 1/8 = 3/8 in. The fourth strip comes out 11 5/8 in.
Then there are the factory edges. They are often dinged from handling and not guaranteed straight, so a careful woodworker trims them first. Take 1/4 in off each long edge and the usable width is 47 1/2 in, before any kerf. Three 12 in strips still fit, and the fourth is 11 1/8 in.
| Plan | Material used | Result |
|---|---|---|
| No kerf, no trim | 48 in | Fits on paper only |
| 1/8 in kerf, no trim | 48 3/8 in | Last strip 3/8 in short |
| 1/8 in kerf, 1/4 in trim per edge | 48 7/8 in from 48 in | Last strip 7/8 in short |
Kerf adds up fast on parts with many cuts. Ten crosscuts with a full-kerf blade turn 1 1/4 in of the sheet into dust, enough to matter on a tight layout.
Trim the factory edges
A clean, straight reference edge is the first cut on any sheet. On a table saw, rip a thin strip off one long edge, then flip the sheet and use the fresh edge against the fence. With a track saw, lay the track a hair in from the factory edge. Every measurement after that comes from the edge you made, not the one the mill sent.
Always keep the blade on the waste side of your mark. On a table saw the fence setting is the distance from the fence to the near side of the blade, so the part between them comes out exactly at the setting and the kerf goes into the offcut.
Kerf and trim in Cortaplan
Open Cutting settings and type your measured Blade kerf, for example 1/8, and the Edge trim to take off every sheet edge. The plan subtracts the kerf from every cut and the trim from every edge, so a part that will not fit is flagged before you cut. The Cut sequence then tells you each fence setting, and the first step reminds you to trim the edges.
Questions
What is the kerf of a standard table saw blade?
About 1/8 in (3.2 mm) for a full-kerf 10 in blade, and about 3/32 in (2.4 mm) for a thin-kerf blade. Check the figure on your blade.
Do I need to account for kerf on every cut?
Yes, on every cut between two parts. The last part on a strip has no cut after it, which is why a plan counts cuts, not parts.
How much should I trim off a plywood sheet?
Enough to get a clean, straight edge, often a fraction of an inch. Take only what removes the damage, the same amount from every edge.