Found out a 2x4 is not actually 2 inches by 4 inches, and I've been mad about it all week
So I'm 4 years into doing this for money and somehow nobody ever sat me down and explained this to me until last Tuesday. I was at the lumber yard over in Tacoma picking up a stack for a deck frame, and the kid at the counter (maybe 19, looked like he just got out of a shop class) asked if I wanted the actual dimensions or the "name" size. I said what? He goes, a 2x4 is really 1.5 by 3.5. A 2x6 is 1.5 by 5.5. It's from planing down rough cut stock, which I guess I knew somewhere in my brain but never actually did the math on. I went home and checked every board in my garage and yep, 1.5 by 3.5 across the board. I've been figuring board feet and spacings off the name size for years and somehow it never bit me hard, which honestly scares me more than if it had. Now I'm wondering what else I've been assuming since day one.
Yeah the 2x4 thing got me too, and I found out pretty much the same way, some guy half my age just casually dropped it on me. What helped me after the initial anger wore off was grabbing a little pocket notebook and actually measuring stuff before I trust the name. I marked down real sizes for 2x4, 2x6, 2x8, 4x4, and even plywood thickness since that's another liar (3/4 ply is not 3/4, it's more like 23/32). Every time I go to the yard now I check a couple boards against my notes because they can vary a little by supplier and how dry the wood is. The spacings thing is real too, I redid my railing math once and was off by almost two inches over eight feet, so it does sneak up on you. Just write it down and keep it in your truck, saves you the headache later.