Material size

From DwarfFortressWiki

Material size is a property of finished goods. It determines how many units of raw material are required to build or construct the finished good, and how many are recovered when it is melted (if possible).

The material size of many (but not all) kinds of objects can be seen in the files in \raw\objects.

[edit] Metal

Material size >= 9 requires 3 metal bars
Material size >= 6 requires 2 metal bars
Material size < 6 requires 1 metal bar