Typically green logs are sawn to 2” X 4” dimensions. The boards are then kiln dried, and planed to the final dimensions (1.5” X 3.5”). The drying and planing are valuable improvements — but, if you really wanted to, you could buy fresh-sawn wet 2 X 4’s.
Similarly, a McDonald’s “quarter-pounder” patty starts out with 4 oz. of raw meat. It weighs significantly less after cooking (about 3 oz.) — but, that’s not considered false advertising, because everyone knows that the 1/4 pound refers to the precooked weight.
so how long is a cubit?
Exactly right.
The boards come out of the sawmill 2” X 4”, and after drying in the kiln,
they are run through the planer mill, where 1/4” is planed off each edge
leaving 1 1/2” X 3 1/2”.
Same for all dimensional lumber...
2X4; 2X6; 2X10; 2X12; 4X4; etc.
Your analogy to the “1/4 pound pre-cooked weight” of a burger is a good one.
Perhaps Lowe’s should say 2” X 4” are the “pre-planed dimensions”