Cut list optimizer· 3 min read
Saw Kerf Explained: Why Many Cuts Leave You Centimetres Short
Every cut turns 1 to 3 mm of wood into dust. With 44 short pieces we show when the kerf costs you a whole extra batten and how to include it in your plan.
You mark eleven pieces of 270 mm on a batten, start cutting — and the last piece comes up short. Your tape is fine. Every cut turns a strip of wood as wide as the saw teeth into sawdust. That strip is the kerf, and with many short pieces it adds up to centimetres.
How much one cut takes
- Japanese pull saw (ryoba) — makers quote a kerf of about 0.7–0.8 mm.
- Thin-kerf blade for a handheld circular saw — for example 1.5–1.6 mm per the manufacturer.
- Standard blades — up to roughly 3.2 mm depending on the blade.
- Angle grinder cutting disc — the thickness is printed on the disc (e.g. 1 mm); the cut will not be narrower.
The exact figure is in the blade's specifications. Even safer: make a test cut in a scrap and measure it with calipers.
Example: 44 pieces of 270 mm
You need 44 identical pieces of 270 mm (about 10 5/8"), say slats for a plant-pot rack. The battens are 3,000 mm long and you trim 5 mm off the start of each to square it. How many battens do you buy?
Without the kerf it would be simple: 11 × 270 = 2,970 mm, so one batten gives 11 pieces and 44 pieces take exactly 4 battens. But eleven pieces mean 10 cuts between them. Together with the squaring cut you need:
| Kerf | Length for 11 pieces | Pieces per batten | Buy | Waste |
|---|---|---|---|---|
| 1 mm | 2,985 mm | 11 | 4 battens | 1 % |
| 2 mm | 2,995 mm | 11 | 4 battens | 1 % |
| 3 mm | 3,005 mm | 10 | 5 battens | 20.8 % |
| 4 mm | – | 10 | 5 battens | 20.8 % |
At 3 mm the eleventh piece is 5 mm short. Each batten gives only 10 pieces, so 44 pieces need 5 battens instead of 4. Only 4 pieces come from the fifth batten, leaving a 1,903 mm offcut. Waste jumps from 1 % to 20.8 %.
Watch the 2 mm case too: eleven pieces fit, but only 3 mm is left at the end. If the batten is a touch short or a cut wanders, the last piece won't make it. A few millimetres of slack per batten is sensible in practice.
Cut list optimizerOpen this example in the cut list calculatorWhy centimetres go missing
A common mistake is to mark all pieces at once from the start of the batten — 270, 540, 810 mm and so on — and cut right on the line. Each cut then takes half its width from the piece before the line and half from the piece after it, so every piece ends up one kerf short. At 3 mm that is 3 mm per piece, or 132 mm of wood across 44 pieces that you had “planned” into them.
How to cut so the pieces fit
- 1Measure and mark one piece at a time from the freshly cut end.
- 2Cut on the waste side of the line — the line stays on the piece.
- 3For a run of identical pieces set a stop on the mitre saw, then you don't measure at all.
- 4Enter your blade's real kerf in the calculator, not a guess.
The calculator adds the kerf between every two pieces and before the offcut at the end of the batten, and the squaring cut once at its start. The offcuts it shows are therefore the lengths you will actually hold in your hand.
Workshop tips
- The shorter the pieces, the more cuts and the more the kerf matters. With two long pieces it hardly counts, with forty short ones it does.
- If you are a few millimetres short of one more piece, try making the pieces 1–2 mm shorter, or skip the squaring cut when the batten end is straight and undamaged.
- Keep offcuts over 250 mm — the fifth batten leaves more than enough for the next job.