Saw kerf is the width of material removed by a cut. A layout must reserve space for that loss between finished pieces. Use the kerf of your actual blade and setup rather than assuming the blade plate thickness is the cutting width.
A two-piece example
Suppose you want two 12-inch-wide panels from an exact 24-inch-wide board. One cut removes material, so both panels cannot finish at 12 inches. With a 1/8-inch kerf, you need at least 24 1/8 inches of usable width for those two panels separated by one cut.
This simplified example assumes clean outer edges and no additional trim cuts. If the board also needs squaring or edge trimming, allow for those operations separately.
Use the measured cut width
Check the blade manufacturer’s specified kerf, then confirm it using a safe test cut on suitable scrap. Compare the original width with the total width of the resulting pieces. The difference is the material removed by that cut. Measure carefully; irregular edges and imprecise measurements can distort the result.
Do not assume every table saw blade removes 1/8 inch. Thin-kerf blades and different tools may remove different amounts. The blade’s plate thickness is not necessarily the tooth cutting width.
Why “number of parts minus one” is only a shortcut
For a simple row of pieces sharing clean outer edges, the gaps between pieces can be counted as one fewer than the number of pieces. Real cutting sequences may need an additional separation cut, edge trimming or breakdown cuts. A two-dimensional sheet layout is more involved than adding a single allowance to a parts list.
Keep finished part dimensions unchanged. Enter kerf as a separate setting so the planner handles it consistently, rather than enlarging every part and then also adding kerf.
Check the plan when the blade changes
If you switch blades or tools, revisit the kerf setting before reusing a layout. A plan that barely fits with one blade can fail with a wider cut. In CutList Pro, set the project’s kerf before optimizing, then verify the resulting dimensions on the actual stock.
For the bigger planning workflow, see how to plan a plywood cutting layout.
Check measurements, material thickness, kerf and grain direction before using a plan. Choose a safe cutting sequence for your tools and material; a diagram is not a substitute for workshop training.