The calculation
A single-cut example
Measure a test piece at 10 in along the axis you will shorten. Make one square cut and measure both resulting pieces along that same axis. If their lengths sum to 9.875 in, the removed material is 10 − 9.875 = 0.125 in. With one cut, the average kerf is 1/8 in, or 3.175 mm.
For three equivalent cuts, a total loss of 0.375 in also gives 0.125 in per cut. More cuts can make a small individual loss easier to measure, provided all pieces and offcuts are included.
Measure the loss you actually intend to model
This method measures average cut loss in your test setup. Blade tooth width, runout and the actual cutting conditions affect the result. A printed blade plate thickness is not necessarily its effective kerf.
Use square parallel cuts for this measurement. An angled cut changes the relationship between the cut face, blade width and the measured axis. Do not apply this formula to a compound or oblique cut without a suitable geometric correction.
Keep other losses out of the test
If an offcut is missing, the calculation counts its entire size as removed material. Sanding, trimming ends, rounding measurements, gaps between pieces and inconsistent measuring directions also distort the estimate. Retain every piece and measure before further machining.
Use the measured kerf in the plywood repeated-parts estimate. Recheck after changing blades or when the measured setup no longer represents the work.
Questions from the workbench
Why does the calculator reject a retained total equal to the starting size?
A positive cut loss is required for this test. Equal or larger totals usually indicate insufficient measurement resolution, mismatched axes or an input error.
Is kerf the same as total project waste?
No. Kerf is the cut loss. End trim, defects, planing and unusable offcuts are separate material losses.
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