What Does 6 4 Mean

6/4 ("six-quarter") means 1.5" of rough thickness before surfacing — half again as thick as the 4/4 baseline, and the size most commonly reached for when a project needs table legs or aprons with real substance to dimension down from.

Why this one specifically

Legs and aprons are usually the first parts cut for a table or case piece, and both typically need to be squared, jointed and planed down from rough stock before final dimensioning — which means starting at 6/4 rather than 4/4 leaves enough material to true up a leg blank and still land at a reasonable finished size (commonly 1.25" to 1.375" square) instead of ending up thin and fragile after milling removes a quarter-4/4's-worth of surfacing loss on every face. That's the practical reason 6/4 gets specified by name on cut lists rather than just "extra-thick 4/4."

What moves the number

The quarter designation itself is fixed; what varies project to project is how much of that 1.5" survives milling. A badly cupped or twisted 6/4 board can lose enough material flattening it that the finished leg ends up closer to 6/4's own surfaced figure of 1.3125" than the buyer expected, which is worth checking before committing a whole set of legs to one board.