From WoodworkersZone WoodWiki
There are just a handful of things you need to know when you head to the hardwood store.
Where to Shop?
Most lumberyards do not have the wood you're after. They target the construction industry and have lumber used to build houses. The big box stores, like Home Depot and Lowes may have some hardwood, but the selection is limited and the prices are usually quite high in comparison.
You're looking for a store that caters to woodworkers. Frank Paxton is one regional vendor paxtonwood.com that sells wood for woodworkers. Try using woodfinder.com to locate a supplier near you.
Mail Order Lumber
There are a few companies that sell wood over the phone or internet. Steve Wall's WallLumber.com is one such supplier.
Most online forums for WWing have an area where members who happen to also be sawyers can peddling their wares.
Some example forums are: WoodNet  and North Carolina WoodWorker . Pen blanks and burls are often best found at the IAP .
The thickness of a board is measured in a unit pronounced “quarters” and denoted “/4”. One quarter is 1/4” in thickness. A board that is “four quarters” thick is 1” thick and is written “4/4”. A board that is eight quarters is written 8/4 and is 2” thick. 12/4 boards are 3” thick.
Some suppliers will start the milling process on your lumber. This can reduce the thickness of a 1” board, yet they still sell it as “4/4”. The board may be closer to 13/16” of an inch. A milled 8/4 board may be about 1 3/4” in thickness.
Wood straight from the tree is considered “rough” lumber. Some suppliers sell rough lumber while many others mill the board, a little bit. This milling, or surfacing, can be on one, two, three or all four sides of the board.
A board noted as “S2S” (Surfaced 2 Sides) has been surfaced on both faces. S3S (Surfaced 3 Sides) boards have both faces milled and one edge.
The Board Foot
Hardwood quantity is measured, and almost always priced by the “board foot (BF).” A board that is 12” wide, 12” long and 1” thick is 1BF of wood. A 1BF board could also be 6x12x2”, or 6x24x1”.
Many project plans will tell you you'll need 20BF of lumber. Be aware that if you buy your wood sight unseen, a supplier could send you many small boards that would still come to 20BF. This could be a problem if your project really needed two large, long boards.
Almost all of the hardwood boards you'll find have been graded. This grade is an objective measure of the quality of the board.
The most common grades you'll encounter, in decreasing quality, are First and Seconds, (FAS), Select (S), #1 Common , #2 Common. Lumber is usually graded from the worst side of the piece.
FAS boards will have the fewest knots, the least amount of sapwood, the best appearance, and the highest yield. Great lumber can come from #1 Common boards, but you may have to work at it, cutting around knots and other defects.
Many retailers charge a premimum for wider boards. For instance, their regular 4/4 hard maple may be priced at $4/BF, but the widest board is 6”. They may price their 10” wide 4/4 hard maple at $4.20/BF.
When buying lumber over the internet, retailers may offer a “UPS bundle”. This is a convenient but small amount of wood (about 20BF) that they can ship within UPS weight restrictions.