Understanding Kerf Loss in Woodworking
Every cut you make with a saw removes material. This material loss—called kerf—is often overlooked during project planning, leading to pieces that come up short or projects that run out of material. Understanding and accounting for kerf loss is fundamental to accurate woodworking.
What Is Kerf?
Kerf is the slot or channel cut by a saw blade as it passes through wood. The width of the kerf equals the set of the blade's teeth plus any wobble or drift during cutting. Every saw cut removes this strip of wood, turning it into sawdust.
Different types of saws produce different kerf widths:
- Standard table saw blades: 1/8" (0.125" or 3.2mm) is typical
- Thin-kerf table saw blades: 3/32" (0.094" or 2.4mm)
- Bandsaw blades: 1/16" to 1/8" (1.6mm to 3.2mm) depending on blade width
- Hand saws: 1/16" to 1/8" (1.6mm to 3.2mm)
- Circular saws: 1/8" to 5/32" (3.2mm to 4mm)
- Track saws: 1/8" (3.2mm) typical
Why Kerf Loss Matters
On a single cut, the difference between accounting for kerf or not might be negligible. But kerf loss compounds quickly with multiple cuts. Consider cutting eight 12-inch pieces from an 8-foot board:
- 8 pieces × 12 inches = 96 inches needed (exactly 8 feet)
- 7 cuts required × 0.125" kerf = 0.875 inches lost
- Total needed: 96.875 inches (more than your 96-inch board!)
That last piece will come up nearly an inch short—a costly mistake if you're working with expensive hardwood or need exact-length pieces.
Cuts vs. Pieces
A common source of confusion is the relationship between cuts and pieces. The number of pieces you get is always one more than the number of cuts:
- 1 cut = 2 pieces
- 2 cuts = 3 pieces
- 4 cuts = 5 pieces
- N cuts = N + 1 pieces
When calculating kerf loss, count the number of cuts, not the number of pieces.
Thin-Kerf Blades: Worth the Trade-off?
Thin-kerf blades remove less material per cut, which sounds like an obvious advantage. However, they come with trade-offs:
- Less stability: Thinner blades can deflect more during cutting
- Shorter lifespan: Less material means less metal to wear
- Slower feed rates: Less body means less rigidity under load
- Reduced cut quality: May leave rougher surfaces on some materials
That said, thin-kerf blades can save material on expensive stock and reduce strain on underpowered saws. They're worth considering when material savings outweigh the downsides.
Measuring Your Actual Kerf
Don't assume your blade's kerf matches the manufacturer's specification. To measure your actual kerf:
- Make a partial cut into a piece of scrap wood
- Use calipers to measure the width of the slot
- Take multiple measurements along the cut to account for any variation
- Use the average for your calculations
Blade wear, arbor runout, and blade wobble can all increase the effective kerf beyond the blade's rated width.
Practical Tips for Managing Kerf Loss
- Always add kerf allowance: When laying out cuts, add the kerf width to each piece length
- Cut longest pieces first: This maximizes your options if something goes wrong
- Mark the waste side: Clearly indicate which side of the line is waste
- Use a cut list calculator: Our Pieces From Stock calculator accounts for kerf automatically
- Buy extra material: Plan for 10-15% waste beyond kerf for defects and mistakes
This kerf loss calculator helps you understand exactly how much material your saw blade will consume before you make the first cut. Enter your board length, number of cuts, and blade kerf width to see the total material loss and remaining usable length.