Board feet in a 2×4×8
There are two honest answers. The wood you actually carry out of the store is 3.50 board feet — a 2×4 really measures 1.5″ × 3.5″. But if you're pricing or trading lumber, the industry counts this board as 5.33 BF, because board feet are by convention figured on the nominal 2″ × 4″ name.
The math, both ways
trade (nominal): 2″ × 4″ × 96″ ÷ 144 = 5.33 BF
Which one do you want? If you're figuring weight, volume, or "how much wood is that really," use 3.50. If you're comparing against hardwood priced per board foot, or reading a mill tally, use 5.33 — the whole trade runs on nominal, for the historical reasons on our nominal vs actual page. (Construction lumber itself is usually priced per piece, so at the store neither number appears on the shelf tag.)
What a 2×4 is for
The 2×4 is the most-manufactured piece of wood on earth — the stud in the stud wall, spaced 16 inches on center behind nearly every drywalled room in North America. Platform framing, which replaced heavy-timber and balloon framing a century ago, is essentially a system for turning bundles of 2×4s into houses with nothing but nails.
Check the shelf tag at the yard and you'll find "precut studs" at odd lengths like 92 5/8″ — that's a 2×4 pre-trimmed so that stud + three horizontal plates equals a standard 8′ 1″ rough ceiling. The 8-foot 2×4 on this page is the general-purpose version of the same board.
Eight feet is the default length — it matches the ceiling, fits inside a pickup bed with the tailgate down, and wastes the least when cut for typical walls. It's usually the cheapest per foot, too, because it's the volume seller.
Heft check: at its true 1.5″ × 3.5″ section, a 8′ board holds 0.29 ft³ of wood — about 10 lb kiln-dried, and closer to 16 lb dripping fresh off the pressure-treated rack.
What that volume costs at hardwood prices
| Price per BF | Actual wood (3.50 BF) | Trade tally (5.33 BF) |
|---|---|---|
| $3.00 | $10.50 | $16.00 |
| $5.00 | $17.50 | $26.67 |
| $7.00 | $24.50 | $37.33 |
| $10.00 | $35.00 | $53.33 |