Board Feet vs Linear Feet vs Square Feet: What's the Difference?
The short answer
A linear foot measures length only: 1 foot (0.30 m) along the piece, no matter how wide or thick it is. A board foot measures volume: a piece 1 inch thick, 12 inches wide and 1 foot long - 144 cubic inches (2.36 L) - calculated as (thickness in × width in × length ft) ÷ 12. A square foot measures area: 12 × 12 inches (0.093 m²) of surface, with no thickness at all.
Lumber sellers use all three, and each one exists for a reason:
- Linear foot - trim, molding, handrail: everything in the bin has the same profile, so length is the only number that matters.
- Board foot - hardwood (oak, maple, walnut): boards come in random widths and thicknesses, so only a volume unit prices them fairly.
- Square foot - sheet goods and flooring: the thickness is fixed, so area is enough.
The three units side by side
| Unit | What it measures | Formula | What’s sold by it |
|---|---|---|---|
| Linear foot (LF) | Length only | length in feet | Baseboard, trim, molding, handrail, framing per stick |
| Board foot (BF) | Volume | (T in × W in × L ft) ÷ 12 | Hardwood lumber from a lumberyard or sawmill |
| Square foot | Area | length ft × width ft | Plywood, drywall, flooring, veneer, decking coverage |
The trap: a linear foot of 1×2 and a linear foot of 2×12 are both “1 linear foot,” but one holds 15 times the wood (actual sizes: ¾ × 1½ in vs 1½ × 11¼ in of cross-section). Linear-foot pricing only works when you’re comparing the same profile.
Board feet: how hardwood is priced
Hardwood thickness is quoted in quarters of an inch - the tally system standardized by the National Hardwood Lumber Association (NHLA). 4/4 (“four-quarter”) is 1 inch, 8/4 is 2 inches. The key rule: board feet are counted on the rough (nominal) thickness, even after the yard planes the board thinner:
| Quarter name | Rough thickness | Typical surfaced (S2S) thickness |
|---|---|---|
| 4/4 | 1 in (25 mm) | 13/16 in (21 mm) |
| 5/4 | 1¼ in (32 mm) | 1-1/16 in (27 mm) |
| 6/4 | 1½ in (38 mm) | 1-5/16 in (33 mm) |
| 8/4 | 2 in (51 mm) | 1¾ in (44 mm) |
So a surfaced 4/4 board measures 13/16 in with your calipers, but you pay for the full 1 inch (NHLA standard surfaced thicknesses). Use the quarter-name thickness in the formula, not what the tape measure says.
Conversion formulas
- Linear feet → board feet: BF = LF × (thickness in × width in) ÷ 12
- Board feet → linear feet: LF = BF × 12 ÷ (thickness in × width in)
- Square feet → board feet: BF = sq ft × thickness in (they’re equal for 1-inch stock)
- Linear feet → square feet: sq ft = LF × width in ÷ 12
Quick cheat sheet - board feet per linear foot of common hardwood sizes:
| Board size | BF per linear foot |
|---|---|
| 4/4 × 4 in | 0.33 |
| 4/4 × 6 in | 0.50 |
| 4/4 × 8 in | 0.67 |
| 5/4 × 6 in | 0.63 |
| 6/4 × 6 in | 0.75 |
| 8/4 × 6 in | 1.00 |
| 8/4 × 8 in | 1.33 |
👉 The Board Foot Calculator does this instantly - enter thickness, width, length and the number of pieces, and it totals the board feet you’ll pay for.
Worked example: a board-foot buy
You want eight red oak boards, 4/4 (1 in) thick, 6 in (150 mm) wide, 8 ft (2.4 m) long:
- One board: (1 × 6 × 8) ÷ 12 = 4 board feet
- Eight boards: 8 × 4 = 32 board feet
- At an example price of $6.00 per board foot: 32 × 6 = $192
Order 15-20% extra (about 37-38 BF). Rough lumber loses volume when you plane it flat, and you’ll cut around knots and checks.
Worked example: a linear-foot buy
Baseboard for a 12 × 10 ft (3.7 × 3.0 m) room with one 3 ft doorway:
- Perimeter: 2 × (12 + 10) = 44 ft
- Minus the doorway: 44 - 3 = 41 linear feet (12.5 m)
- Plus ~10% for miter cuts: about 45 LF → six 8 ft sticks
Notice thickness and width never entered the math - that’s the whole point of a linear foot. The Baseboard Calculator runs this from your room size, with doors subtracted and waste included.
Watch-outs
- Nominal is not actual. A softwood “2×4” actually measures 1½ × 3½ in (US DOC PS 20, the American Softwood Lumber Standard). Hardwood plays the same trick in reverse: surfaced 4/4 measures 13/16 in but is tallied at 1 in. Use nominal numbers for pricing, actual numbers for fitting parts.
- A board-foot price only compares within a thickness. $6/BF for 4/4 walnut and $6/BF for 8/4 walnut are different deals - thicker stock usually carries a premium per board foot. Compare like with like.
- Square feet ignore thickness entirely. 100 sq ft of ¾-in plywood and 100 sq ft of ¼-in plywood are the same square footage but three times the wood. Always pair a square-foot quote with a thickness.
- Length goes into the BF formula in feet, not inches. Mixing the two is the classic mistake - it throws the total off by a factor of 12.
Related
- Board Foot Calculator - board feet from thickness, width, length and piece count.
- Walls & ceilings tools - the full walls toolset.
- Half-inch vs five-eighths drywall - the sheet-goods version of this decision: same square feet, different thickness.
- How far can a 2×8 deck joist span? - where those nominal lumber sizes end up doing structural work.