> The limited availability of lumber and the rapid pace of housing construction made other methods like concrete-block housing viable. This pressured further compromise because thinner 2x4s were a way to compete in price with wood alternatives. Size standards, maximum moisture content, and nomenclature were agreed upon only as recently as 1964. The nominal 2x4 thus became the actual 1½ x 3½, imperceptibly, a fraction of an inch at a time.

http://www.harvarddesignmagazine.org/issues/45/nominal-versu...

So it seems the reduction was was driven by cost saving, not a product of the finishing process, and it's actually only been standardized that way for 58 years.

"Dimensional lumber is available in green, unfinished state, and for that kind of lumber, the nominal dimensions are the actual dimensions."

Your quote just means when you're buying green wood and it says it's 2"x4" it will be exactly 2"x4". It doesn't mean a 2x4 started out as a 2"x4" green board.

I was originally pointing out that the naming is simply a standard and convention, 'dimensional lumber'. All that matters is that if I buy a '2 by' almost anywhere in the United States, it will be close to the same size and characteristics.

canada has no hope of doing anything in metric here, everything is in US units, and probably will be until the year 2200

(I rounded those values because if the US were to go metric, the dimension would slightly change, rather than being exactly 50.8 by 101.6 mm)

What I tried to convey, in a stupid way, is that there wouldnt be an exact translation of the measurements into metric, but that the dimensions qould slightly change in switching over.

and now I realize that that point was irrelevant anyways. Sorry for derailing the thread with useless replies.