Quick answer
How Many Board Feet in a 4x4?
A 4x4 holds 1.333 board feet per linear foot — the same per-foot rate as a 2x8, since both are 8 square inches in cross section. So an 8-foot 4x4 is 10.67 board feet (4 × 4 × 8 ÷ 12).
The 4x4 is the only square stick in this group, and that changes how I think about it. A joist or stud lies flat and carries load across its depth; a 4x4 stands up and carries load straight down its 3.5″ × 3.5″ column. It shares the 1.333 BF/ft rate with a 2x8 — same 8 square inches of cross section — but you'll never confuse the two on site. If the matching number between a square post and a wide joist seems strange, the reason is just geometry, and it falls straight out of the board foot formula.
How many board feet are in a 4x4 by length?
At 1.333 BF per foot, here are the common post lengths:
| 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 |
Is a 4x4 really 4 inches?
No — a surfaced 4x4 measures 3.5″ × 3.5″, shedding ½″ on each of its four faces exactly the way a 2x4 loses its width. So the stick is square but smaller than its name, and you still calculate board feet on the nominal 4×4 because softwood posts are priced by the nominal call. One wrinkle I always flag at the counter: rough-sawn and some heavy pressure-treated 4x4s can come closer to a full 4″ so if a post has to fit a hardware bracket, measure the actual piece. The half-inch loss follows the same pattern explained in nominal vs actual dimensions.
How many board feet are in a 4x4 fence?
Posts are the 4x4's main job, so here's a fence I'd quote. A 48-ft run with posts every 8 ft:
- 48 ft ÷ 8 ft + 1 = 7 posts, each 8 ft (2 ft buried, 6 ft above grade).
- 7 × 8 ft = 56 linear feet → 56 × 1.333 = ~75 board feet of 4x4.
At a treated-post rate around $1.10 per board foot (a planning estimate — treated 4x4 is wet and heavy, and pricing reflects it) that's roughly $82 in posts before a single rail or picket. Treated 4x4s also arrive soaked, so order a little early and let them dry before final cuts. For a full fence or pergola takeoff I list posts, rails, and pickets in the cut list calculator and price the lot in the lumber cost calculator.
What are 4x4s used for?
The 4x4 is the everyday post: deck and porch posts, fence posts, pergola and arbor legs, mailbox and sign posts, and light structural columns. Step up to a 6x6 (3.0 BF/ft, 5.5″ square) when a post runs tall, carries a beam, or local code calls for it. Because a 4x4 packs 1.333 BF into every foot, a run of tall posts adds up fast — a dozen 10-ft posts is 160 board feet — so it's worth tallying rather than guessing. Building flat instead of vertical? A 2x4 handles wall framing at a fraction of the wood per foot.
Frequently asked questions
Is a 4x4 really 4 inches?
No. A surfaced 4x4 measures 3.5″ × 3.5″ losing ½″ on each face the way a 2x4 loses width. You still calculate board feet on the nominal 4×4 because softwood is priced that way. Rough or some treated 4x4s can run closer to a full 4″ so measure if it must fit hardware.
How many board feet are in a 4x4 fence?
A 48-ft fence with posts every 8 ft takes about 7 posts, each 8 ft, or 56 linear feet. At 1.333 BF/ft that's roughly 75 board feet of 4x4 for the posts alone, before rails and pickets.
What is the difference between a 4x4 and a 6x6 post?
A 4x4 holds 1.333 BF/ft and surfaces to 3.5″ square. A 6x6 holds 3.0 BF/ft and surfaces to 5.5″ square — more than twice the wood per foot — so it's used for taller or more heavily loaded posts and beams.