Rough wood, at one stage of its trip to your shop, is reckoned in 1/4"
increments in nominal thickness ... or thereabouts.
IOW, a 5/4 (five quarter) board would measure 1 1/4" in nominal thickness, a
12/4 board 3" in nominal thickness, and so on..
A 4/4 board, sold as "dimensioned lumber", or after you have joined and
planed it, would have an actual finished thickness of 3/4".
In figuring board feet, lumber retailers sell you 3/4" thick "dimensioned
lumber", but calcuate the board feet using the 4/4 "nominal" thickness.
For sheet goods, like decking, all bets are off and it is not necessarily
the same. 5/4 decking is usually about 1 1/16" in finished thickness, IME.
There's more to it, but that should get you started in tlaking the lingo at
a hardwood lumber yard.
Last update: 7/28/03
Click to see the full signature.