Board feet in a 4×4×10

There are two honest answers. The wood you actually carry out of the store is 10.21 board feet — a 4×4 really measures 3.5″ × 3.5″. But if you're pricing or trading lumber, the industry counts this board as 13.33 BF, because board feet are by convention figured on the nominal 4″ × 4″ name.

The math, both ways

Which one do you want? If you're figuring weight, volume, or "how much wood is that really," use 10.21. If you're comparing against hardwood priced per board foot, or reading a mill tally, use 13.33 — 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 4×4 is for

The 4×4 is the fence and deck post — nearly always pressure treated, because posts meet dirt. Treated ratings matter here: "ground contact" stock carries roughly twice the preservative of "above ground" boards, and a post set in concrete needs it.

Its 3-1/2″ actual dimension is why post-base hardware, anchors, and caps all say "for 4×4 (3-1/2″)". Building codes have been steadily pushing decks toward 6×6 posts, so check span tables before framing anything tall on 4×4s. Unlike smaller sizes, a 4×4 usually contains the tree's center — expect checking cracks as it dries, which look alarming and are mostly cosmetic.

Ten-footers are the remodeler's length: enough extra to clear a 9′ ceiling, cut around a split end, or get two 57″ pieces with margin. Many yards price them barely above 8′ stock, making them quiet bargains per usable foot.

Heft check: at its true 3.5″ × 3.5″ section, a 10′ board holds 0.85 ft³ of wood — about 30 lb kiln-dried, and closer to 47 lb dripping fresh off the pressure-treated rack.

What that volume costs at hardwood prices

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Related: 4×4×8 · 4×4×12 · all sizes