Quick answer
How Many Board Feet in a 2x8?
A 2x8 holds 1.333 board feet per linear foot. So an 8-foot 2x8 is 10.67 board feet (2 × 8 × 8 ÷ 12). Multiply 1.333 by the length in feet, or read the chart below.
The 2x8 is where the width-loss surprise lands hardest, and I've taken the phone call more than once: "Nathan, these joists came in narrow." They didn't. A 2x8 is supposed to be 7¼″ wide, not 7½″ and that missing quarter-inch is built into the standard. The board feet, though, still ride on the nominal label — 1.333 per foot — and if that split between what you measure and what you pay for feels odd, the board foot calculation guide shows exactly where it comes from.
How many board feet are in a 2x8 by length?
At 1.333 BF per foot, a 2x8 carries a third more wood than a 2x6 of the same length:
| Length | Board feet |
|---|---|
| 6 ft | 8.00 |
| 8 ft | 10.67 |
| 10 ft | 13.33 |
| 12 ft | 16.00 |
| 14 ft | 18.67 |
| 16 ft | 21.33 |
Why is a 2x8 only 7¼ inches wide?
Here's the detail that separates the 2x8 from the narrower sizes: any nominal board wider than 6 inches loses ¾″ in surfacing, not the ½″ a 2x4 or 2x6 gives up. So a 2x8 finishes at 7.25″ not 7.5″. That extra quarter-inch matters when you're fitting a ledger or matching old joists, but it does not change the board foot math — you still calculate on the nominal 2×8 because that's how softwood is priced. The full pattern, including why the cutoff sits at 6 inches, is in nominal vs actual dimensions.
How many board feet are in a 2x8 floor?
Floor joists are the 2x8's home turf, so picture a 12 ft × 12 ft room framed 16″ on center:
- Joists span the 12-ft width → about 10 joists, each 12 ft long = 120 linear feet.
- Two rim joists at 12 ft each = 24 linear feet.
- 144 linear feet × 1.333 BF/ft = ~192 board feet of 2x8.
At a joist-grade rate around $0.70 per board foot (a planning estimate — #2 SYP and SPF move weekly) that frame is roughly $134 in 2x8. A double 2x8 header over a 6-ft opening, by contrast, is just 12 linear feet, about 16 board feet. I keep both kinds of takeoff — repetitive joists and one-off headers — in the cut list calculator so the rim, blocking, and headers don't get forgotten.
What are 2x8s used for?
The 2x8 is the first true load-carrying joist size most builders reach for: floor joists, deck joists, stair stringers, and shallow built-up headers. The added depth over a 2x6 buys span, which is why second-floor and deck framing leans on it. Because a single 12-ft piece is already 16 board feet, a full floor moves the material budget noticeably — worth pricing in the lumber cost calculator before you commit to a joist size.
Frequently asked questions
Why is a 2x8 only 7.25 inches wide instead of 7.5?
Nominal boards wider than 6″ lose ¾″ in surfacing rather than ½″ so a 2x8 finishes at 7.25″. The board foot math still uses the nominal 2×8 because softwood is priced by nominal size, but the face you fasten is 7.25″ wide.
How many board feet are in a 2x8 floor?
A 12 × 12 ft floor framed with 2x8 joists 16″ on center takes about 10 joists plus two rim joists — roughly 144 linear feet. At 1.333 BF/ft that's about 192 board feet for the floor frame.
How many board feet are in a double 2x8 header?
A double 2x8 header over a 6-ft opening is two boards 6 ft long, or 12 linear feet. At 1.333 BF/ft that's about 16 board feet, before the king and jack studs around the opening.