board thickness in quarters

"Quarters" is how big the rough board is *before* they start planing it. So a 2x4 starts off with a 2" by 4" rough blank, then they plane it flat and smooth, resulting in a 1.5" by 3.5" final board.

If it's sold as "8/4" that will be a rough-sawn dimension and if you buy rough sawn that will indeed be the dimension give or take the tolerance of the sawmill and any shrinkage post-mill.

When you buy construction lumber, for example a 2x4, that's also a rough sawn dimension but what you buy is not rough sawn lumber, and there are accepted dimensional standards for construction lumber intended to allow lumber from different suppliers to be interchanged on a job--those standards will have a 2x4 being 1.5x3.5 after being planed to final dimension.

What amazes me is that they have to take a half inch off before they get a straight smooth board. I guess its because they standardized on that size, but still, thats a lot of waste.

They don't start with a 2"x4" chunk of wood anymore.

Somewhere between 1 and 1 1/4 IME.

If it's rough sawn hardwood, it's 8/4. Also note that 2x8 dimensional lumber isn't 1-1/2 x 7-1/2, as you might infer from a 2x5, rather

Rough sawn, yes. Once it's planed it'll no longer be 2" thick, though it will still be called 8/4 S2S, or some such.

A 1" thick piece planed down to 3/4", most likely. If its rough sawn it'll be 1" thick.

The best reason going; a bar bet. ;-) We used to call the local library's reference librarian. They loved settling bar bets. ;-)

The "quarter" measurement standard generally only applies to hardwoods (and sometimes softwood decking). The actual thickness of 4/4 lumber depends on whether its rough, S1S, or S2S. (And to a certain extent, the specific case...a quick google search for "4/4 S2S" shows results from 13/16" to 15/16".)

Dimensional softwood construction lumber has its own set of rules and is listed as nominal sizes even though the actual sizes can be up to 3/4" smaller.

Wikipedia has a decent entry:

Chris has it right ... hardwood and softwood construction lumber are treated differently, in all dimensions, width, length and thickness, as well as in allowable defects per classification.

The obvious necessity for standardized sizing in construction material makes it a much more reliable "standard" ... IOW, when planning a construction project you really need to be able to count on a tubafour being indeed 1 1/2" x 3 1/2", etc.

On Mon, 14 Dec 2009 14:23:28 -0600, the infamous homer scrawled the following:

Erm, you think tubafores are _straight_, Homey? Call this number:

P.S: They're cut when green and wet, so cellular shrinkage accounts for some of that loss, too.

-- Every day above ground is a Good Day(tm). -----------

They don't start with a 2"x4" chunk of wood anymore.

Correct, most mills that kiln dry have a target green size of 1.75" after drying this leaves about 1.625" for planing.

Doug fir mills on the left coast that process all their wood green usually have a target thickness of 1.562"

basilisk

There's at least ONE area that definitely improves when going metric.

If you want to have it planed on all sides, it's known then as 45x95 (mm) - it's then really that. Then if it's dimensioned (not necessarily fully planed), it's

Same rules apply to all sizes, i.e. you can also get fully planed

How's that fundamentally any better than standard-sized construction lumber? It's simply a different set of numbers for the same thing.

What primarily (imo) screws up stuff in the US is all the imported crap that's metric instead of US or the "chintzing down" of historical sizes like ply thicknesses by a less-32nd and so on. Hard to imagine such cost-shaving tactics don't go on on the other side of the pond(s), too...???