Board feet in a 2×10×20

There are two honest answers. The wood you actually carry out of the store is 23.13 board feet — a 2×10 really measures 1.5″ × 9.25″. But if you're pricing or trading lumber, the industry counts this board as 33.33 BF, because board feet are by convention figured on the nominal 2″ × 10″ name.

The math, both ways

Which one do you want? If you're figuring weight, volume, or "how much wood is that really," use 23.13. If you're comparing against hardwood priced per board foot, or reading a mill tally, use 33.33 — 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 2×10 is for

The 2×10 carries floors: around 15–16′ of span at 16″ on center in the strong species, which covers most rooms in most houses. It's also the standard stair-carriage material where the 2×12 won't fit, and — doubled or tripled — the built-up beam under countless decks.

Old-house owners meet the 2×10's ancestors during remodels: joists in pre-1960s homes often measure a true 2″ × 10″ (or close), so sistering a modern 9-1/4″ board against one means shimming. Lumber history shows up as a gap at the subfloor.

Twenty-footers are the frontier of stock lumber — many yards keep a few, others make them a special order. They exist for the spans where a splice would be a sin: long floor joists, ridge boards, and built-up beams. At this length delivery stops being a luxury; so does a helper. The consolation: one uncut 20′ board is often cheaper, straighter, and stronger than the two shorter boards plus splice hardware it replaces.

Heft check: at its true 1.5″ × 9.25″ section, a 20′ board holds 1.93 ft³ of wood — about 67 lb kiln-dried, and closer to 106 lb dripping fresh off the pressure-treated rack — a genuine two-person lift.

What that volume costs at hardwood prices

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Related: 2×10×8 · 2×10×10 · 2×10×12 · all sizes