Foam board thickness
Every wall and divider in an insert uses one board thickness. If your board is 4.8 mm and you plan for 5 mm, the errors add up across every wall.
Common sizes
- 3/16 in (4.76 mm): the usual craft-store board in the US. For example, Elmer's 20 × 30 in foam board is listed as 3/16 in (distributor listing).
- 5 mm: common in Europe and in many published insert plans. Builders often treat it as interchangeable with 3/16 in, but it is 0.24 mm thicker per wall.
- 3 mm and 1/8 in (3.18 mm): lighter boards for small token trays.
- 10 mm and 1/2 in (12.7 mm): heavy boards for large bases.
Sheets are commonly sold at 20 × 30 in in the US and A-sizes (A3, A2, A1) in Europe. The designer estimates how many sheets you need for each.
Measure your board
A single board is hard to measure with a ruler. Cut a few strips, stack them face to face, measure the stack, and divide by the number of strips.
How thickness changes the cut list
For a 2-compartment tray with walls on the base and compartments of 60 + 60 × 90 mm:
- 5 mm board: base 135 × 100 mm, short walls 90 mm long.
- 4.76 mm board: base 134.29 × 99.53 mm, short walls 90 mm long.
The tray is 0.7 mm narrower with the thinner board. In a box with several trays side by side, that difference can decide whether the insert fits.