Most beginners think waste in plywood comes from cutting parts wrong. Experienced woodworkers know better: most waste comes from kerf - the slot of material your saw blade removes on every single cut. Kerf is invisible, predictable, and unforgiving. Plan for it, or lose a sheet of plywood every five projects.
What is kerf, exactly?
When a circular blade or band saw blade passes through wood, it doesn't just split the material - it removes a strip of wood the width of the blade's teeth. That strip is the kerf. A standard 10-inch table saw blade has a kerf of about 3.2mm (1/8"). A thin-kerf blade is around 2.4mm. A track saw plunge blade is typically 2.2mm.
The kerf doesn't sound like much. But multiply it by the number of cuts in a typical project and the math gets ugly fast.
The kerf math on a real project
Take a kitchen cabinet build with 42 parts. To make 42 parts from 4×8 ft plywood sheets, you'll typically make somewhere between 80 and 120 cuts (each part needs 2-4 cuts depending on layout efficiency). Let's say 100 cuts at 3.2mm kerf each.
100 cuts × 3.2mm = 320mm of plywood literally turned into sawdust.
If your sheets are 1220mm wide, that's 26% of one full sheet of plywood - gone, before you've even thought about layout inefficiency. On a $50 sheet of cabinet-grade plywood, that's $13 in dust.
Why optimizers need to know your kerf
A 2D bin-packing algorithm that ignores kerf will tell you that two 1220mm parts fit perfectly across a 2440mm sheet. They don't. Once you make the cut between them, you've lost 3.2mm of width - and one of those parts is now 1216.8mm. If your design requires 1220mm exactly, you've ruined a part and need to start over.
A good cut list calculator includes kerf in every adjacency calculation. The optimizer sets up parts with the kerf gap built in, so the diagram you take to the saw is the diagram that actually fits the wood.
How to set kerf accurately
You don't have to guess. Measure your blade:
- Find the blade's product specs - the kerf is usually printed on the box or stamped on the blade body.
- If the spec is missing, measure: cut a scrap, then measure the gap with calipers. The gap is your kerf.
- For dado blades, kerf equals the dado stack width.
- For laser cutters, kerf is around 0.1-0.3mm depending on material - much smaller, but still worth setting accurately.
Common values to memorize:
- Stock 10" table saw blade: 3.0-3.2mm (1/8")
- Thin-kerf 10" blade: 2.2-2.4mm (3/32")
- Track saw plunge: 2.2mm
- Bandsaw: 0.6-1.0mm (varies wildly)
- Hand saw: 1.0-1.5mm
The trick most calculators miss
Edge banding adds material back. If you're using 0.5mm iron-on banding on two long edges, your finished part is 1mm wider than the cut size. Some optimizers let you specify "finished size" vs "cut size" - if yours doesn't, subtract the banding thickness from your input dimensions before optimizing.
When kerf doesn't matter
Three cases:
- Single-cut parts. If a part comes off a sheet with one cut and the rest is offcut, kerf is irrelevant for that part.
- Rough cuts you'll trim later. Cutting parts oversized to be re-trimmed by a router or jointer? Kerf disappears in the trim allowance.
- Different materials. Foam, plastic, and very thin sheet goods have different cutting dynamics - kerf may not be uniform across the cut.
For everything else, set the kerf in your cut list optimizer accurately and trust the diagram.
Bottom line
If your project uses three or more sheets of plywood, kerf is the single biggest controllable source of waste in your build. Two minutes spent measuring your blade and entering the right number into the optimizer is worth $10-30 in saved material on a typical kitchen or built-in. Stop ignoring it.
Try the cut list calculator with your blade's actual kerf. Or pick a project template - kerf is pre-set on every one.