A 4/4 board is one inch even when it measures 13/16″. A 2×4 is figured as 2×4 even though it is 1½ × 3½. Both are normal, both are billed that way, and this shows you the gap.
A board foot is 144 cubic inches — a piece one inch thick, twelve wide and twelve long.
bd ft = T″ × W″ × L″ ÷ 144 or T″ × W″ × L(ft) ÷ 12
It is a volume measure, not a length or an area, which is why two boards with completely different proportions can cost the same.
Hardwood is sold in quarters of an inch of rough thickness. 4/4 is one inch, 5/4 is an inch and a quarter, 8/4 is two inches. The mill saws to that thickness green, and everything after — drying, surfacing, straightening — takes material away from it.
| Called | Rough | After S2S | You lose |
|---|---|---|---|
| 4/4 | 1″ | 13/16″ | 19% |
| 5/4 | 1¼″ | 1 1/16″ | 15% |
| 6/4 | 1½″ | 1 5/16″ | 13% |
| 8/4 | 2″ | 1¾″ | 13% |
| 12/4 | 3″ | 2¾″ | 8% |
You are charged on the rough figure. That is not a swindle — it is the wood the mill actually cut, and the surfacing is work done on your behalf. But it means a hundred board feet of surfaced 4/4 gives you about eighty-one board feet of usable material, and any cutlist built from finished dimensions needs to allow for it.
A 2×4 is figured as two inches by four inches. It measures 1½ by 3½. That is a third of the volume gone, and it is why a nominal board foot figure on framing lumber overstates what arrives on the truck by about thirty percent.
Softwood is mostly sold by the piece or the lineal foot, so this rarely bites. It bites when you are pricing a large framing package by the thousand board feet, or comparing a hardwood quote against a softwood one.
Rough hardwood is not a sheet good. Boards have wane, checks, knots and bow, widths are random, and grain matching means rejecting perfectly sound material for looking wrong next to its neighbour.
Ten percent is enough on softwood cut to length. Twenty-five is a sensible default for furniture from rough stock. Forty is not unusual on figured or narrow stock, or when every face has to match.
One board foot is a twelfth of a cubic foot, so weight per board foot is simply density over twelve. Red oak at 44 lb/ft³ is about 3.7 lb a board foot — a hundred board feet is 370 lb, which is a real consideration for a half-ton pickup once you have added a toolbox and a passenger.
Green lumber runs far heavier, sometimes half again, because the water has not left yet.
No. A lineal foot is length alone. A board foot is volume. A 1×12 gives one board foot per lineal foot; a 1×6 gives half.
Before, for pricing. Hardwood board footage is figured on rough thickness and, under NHLA rules, on the width at the narrow end for random-width stock.
Almost always the two effects above stacking: rough-to-surfaced loss, then cutting waste. A hundred rough board feet of 4/4 is closer to eighty-one surfaced, and after a normal twenty-five percent cutting loss you are working with about sixty.