Board feet in a 4×6×8

There are two honest answers. The wood you actually carry out of the store is 12.83 board feet — a 4×6 really measures 3.5″ × 5.5″. But if you're pricing or trading lumber, the industry counts this board as 16.00 BF, because board feet are by convention figured on the nominal 4″ × 6″ name.

The math, both ways

Which one do you want? If you're figuring weight, volume, or "how much wood is that really," use 12.83. If you're comparing against hardwood priced per board foot, or reading a mill tally, use 16.00 — 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 4×6 is for

The 4×6 is beam stock: window and door headers in western framing, deck beams, swing-set crossbars, timber steps, and the outdoor project that wants to look substantial. East of the Rockies builders usually nail up headers from doubled 2×6s; the West, with its big-timber mills, kept the solid-sawn tradition.

The comparison worth knowing: a built-up double 2×6 is 3″ thick while a solid 4×6 is 3-1/2″ — the solid beam fills a 2×4 wall's width perfectly with no plywood spacer. Like all timbers it's usually sold green or barely dried, so expect checking as it seasons, and expect real weight on the tailgate.

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 3.5″ × 5.5″ section, a 8′ board holds 1.07 ft³ of wood — about 37 lb kiln-dried, and closer to 59 lb dripping fresh off the pressure-treated rack.

What that volume costs at hardwood prices

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Related: 4×6×12 · all sizes