Start with the sheet you will buy
A nominal 4×8 sheet of plywood or MDF is 48 by 96 inches, 4,608 square inches. A metric sheet is often 1,219 by 2,438 mm, a little under 48 by 96. If the last part is close to the edge, measure the sheet in the rack. The sheet goods calculator uses the width and height you type, not the name on the unit price.
Trim is the strip you cut off a factory edge before any part is placed. Type zero when that edge is staying on the project. Trim comes off both sides, so ½ inch of trim on a 48 inch edge leaves 47 inches of usable width.
Kerf is wood the parts do not include
A full-kerf table-saw blade is about ⅛ inch (3.2 mm). A thin-kerf blade is closer to 3/32 inch (2.4 mm). The tooth path sits between parts. It is not part of either rectangle.
Along one 96 inch edge, how many 24 inch strips come off? With no kerf, 96 ÷ 24 = 4. With an ⅛ inch kerf, each cut after the first consumes the strip plus the tooth path. The count is the whole number of times 24⅛ fits into 96 plus one kerf, which is 3 strips, not 4. The kerf and yield calculator is that one-direction count: pieces in a row, with a kerf between them and none after the last.
Count = the whole number of (piece + kerf) that fit in (length + kerf)
A cut list on a full sheet
Four rectangles, each 24 by 48 inches. Their area is 4,608 square inches. The sheet is 4,608. On area alone they fill it, and with the kerf set to zero the layout uses 1 sheet. Nothing is left over.
Set the kerf to ⅛ inch and leave the parts free to rotate. The same four rectangles need 2 sheets. The blade took the margin that made the fourth part fit. Area cannot see that. The layout can: each part sits on a shelf, and the next part on that shelf has to clear the kerf.
| Cut list | Kerf | Sheets |
|---|---|---|
| Four 24 × 48 on a 48 × 96 | 0 | 1 |
| The same four parts | ⅛ in | 2 |
| 24 in strips along 96 in | ⅛ in | 3 strips, not 4 |
Unused share on the kerfed layout is about 50 percent of the sheets you buy. Kerf and the offcut around the parts both count as unused. The drawing on the calculator is to the sheet’s own proportions. Buy from the sheet count, not from a part that looks as if it might squeeze.
What a sheet estimate will not decide
- Rectangles only. Curves, mitres, and bookmatched veneer are not packed.
- The layout is a shelf heuristic. A careful pencil drawing can sometimes do better with mixed sizes.
- Grain that must run one way has to be locked. A rotated part is a different part if the face veneer shows.
Questions
Why do four parts that fill the sheet on paper need a second sheet?
Four 24 by 48 inch rectangles are exactly a 48 by 96 sheet only when the blade removes nothing. An ⅛ inch kerf between them uses wood the rectangles do not include. The fourth part no longer fits, and the sheet count goes from one to two.
Should I rotate a part to save a sheet?
Only when the grain may run either way. Plywood face veneer usually has a direction you care about. Lock rotation on those parts. If the locked orientation does not fit the sheet, the calculator reports the part as unpacked instead of turning it.
Is a 4×8 sheet exactly 48 by 96 inches?
A nominal 4×8 is usually sold as 48 by 96 inches. A metric sheet is often 1219 by 2438 mm, a little under that. Measure the sheet you bought if the last part is close. Trim is whatever you cut off each factory edge before the layout starts. Use zero if that edge stays.
Does the sheet count include curves and mitres?
No. The layout is rectangles. Curves, mitred edges, and bookmatching are not in it. It is also a shelf layout, not a proof that a person with a pencil cannot pack the same parts tighter.