Board feet and buying rough lumber

Rough lumber is sold by volume, not by length, and the unit is the board foot: one foot square and one inch thick. The formula is thickness in inches, times width in inches, times length in inches, divided by one hundred and forty four.

That divisor is just the number of cubic inches in a board foot. A board eight inches wide, six feet long and one inch thick works out at four board feet. Once the arithmetic is familiar it takes a few seconds at the rack and it stops you guessing.

Quarters, and why a one inch board is not one inch

Rough stock is quoted in quarters of an inch. Four quarter is nominally one inch, eight quarter is two. Those are sawn dimensions, measured green and before anything was planed, so a four quarter board that has been dried and surfaced on two faces will arrive closer to thirteen sixteenths. Plan the project around the thickness you will actually have, not the number on the label.

What to look at before the price

Sight down the length of the board on edge and then on face. Bow along the length can often be worked around. Twist, where the two ends sit in different planes, is the one to avoid, because flattening a twisted board costs you thickness everywhere.

Check the end grain too. Tight, closely spaced growth rings running roughly perpendicular to the face mean quarter sawn stock, which moves far less with humidity and is worth paying for on a tabletop. Rings running parallel to the face mean flat sawn, which is cheaper, often more figured, and more inclined to cup.

Finally, buy more than the cutting list says. Somewhere between fifteen and thirty per cent extra covers the defects you cut around and the piece you get wrong, and a second trip rarely finds boards that match the first.