Board Foot Calculator: How to Calculate Board Feet

How to measure lumber for board feet

1. Thickness. Nominal for softwood (2 in for a 2x4), the quarter size for hardwood (4/4 is 1 in, 8/4 is 2 in).
2. Width in inches. Nominal for dimension lumber (4 for a 2x4); the full measured width for rough hardwood. For random widths of one length, enter the total width as 1 board.
3. Length in feet (8 ft 6 in is 8.5). PS 20 sets softwood lengths in multiples of 1 or 2 ft, and the Wood Handbook says 2 ft multiples are common for most construction lumber. NHLA standard hardwood lengths run 4 to 16 ft.
4. Number of boards and extra. Extra, 0 by default, is your own allowance for defects and offcuts; no source we checked gives a standard figure.

Board feet chart for common lumber sizes

Board feet per piece for nominal softwood sizes (PS 20 board measure):

Multiply by the count: twenty 2x6s 12 ft long are 20 × 12 = 240 board feet. To count the pieces first, use the wall stud calculator for studs and plates or the fence calculator for posts, rails, and pickets.

Nominal vs actual size: why a 2x4 isn't 2 by 4 inches

PS 20, the American Softwood Lumber Standard, defines nominal size as "The label designation for lumber size categories that does not reflect the dressed size," noting that "a dry 2 by 4 is surfaced to 38.1 mm by 88.9 mm (1 1/2 by 3 1/2 inches)." A NIST article explains that nominal sizes came from rough lumber before it was surfaced at the mill.

Board measure still counts the nominal size; the UW fact sheet notes that "our board-foot calculation results in the nominal volume, not the true volume" (6.875 board feet for its 10 ft 2x6). Dry sizes from PS 20 Table 3, for 8 ft pieces:

Enter the nominal size to match a lumber tally; use the actual size only for the true volume of wood.

Hardwood: 4/4, 5/4, 8/4

Hardwood thickness is named in quarter inches: NHLA rules express lumber 1 in and thicker as 4/4, 5/4, 6/4 and up to 24/4, and AHEC gives 4/4 as 1 in and 8/4 as 2 in. These are rough thicknesses. NHLA paragraph 16 says: "In surfaced lumber, board footage is measured before surfacing." So a 4/4 board planed to 13/16 in still counts as 1 in.

Under 1 in, the standards differ. NHLA paragraph 16 measures standard hardwood thicknesses under 1 in as 1 in (paragraph 18 counts such lumber, except squares, by surface measure), while PS 20 uses the "fraction of an inch" for softwood. So the calculator starts at 1 in; for a 1/2 in softwood board, halve the 1 in result.

How a hardwood tally rounds board feet (NHLA)

4 board feet, not 4.17, for a 4/4 board 6 1/4 in wide and 8 ft long on an NHLA tally. NHLA paragraph 16 figures surface measure as actual width (in) × standard length (ft) ÷ 12, "rounded up or down to the nearest whole number," drops "any fractions of feet longer than the standard lengths," and multiplies the surface measure by the thickness. The calculator keeps the decimals:

Rounding goes both ways: the 8 3/4 in board gains a sixth of a square foot, and the 8 ft 6 in board is tallied on 8 ft because NHLA standard lengths are whole feet from 4 to 16 ft. Surface measures that land on an exact half foot are counted "alternately to the next higher or lower foot." To check a mill tally, run the calculator per board, or with the total width of boards of one length and thickness, and expect small differences from this rounding.

How lumber is sold

Board feet are the trade unit: PS 20 calls a board foot "the unit of measurement of lumber," and NHLA uses it too. Panels such as plywood and OSB are counted by the sheet instead; see the plywood calculator. At retail, NIST Handbook 130's method of sale rules apply in states that adopt them (about 46 at last count, says the American Wood Council):

• Softwood (surfaced): the number of pieces, the minimum dressed or actual width and thickness, and each piece's length or the lineal footage. Nominal sizes must be marked "nominal" or "nom" with the actual or minimum dressed sizes displayed.
• Hardwood (not flooring or molding): by linear measure or by count, with the surfaced width and thickness (and, for count, the length) stated, or "by surface measure (square feet) when a thickness is stated."
• Random-width kiln-dried hardwood: "net board footage with no addition of footage for kiln drying shrinkage or surfacing."

AHEC notes that a buyer of kiln-dried lumber sold on a green tally, measured before kiln drying, can expect about 7% fewer board feet because of shrinkage. Ask how your dealer measures (piece, linear foot, square foot, or board foot) and whether a hardwood tally is green or net.

Board feet in a log: Doyle, Scribner, and International 1/4-inch rules

64 to 95 board feet in a 16 ft log 12 in across the small end, depending on the log rule: 64 by Doyle, 80 by Scribner Decimal C, and 95 by International 1/4-inch (Virginia Tech, Table 1). UT Extension defines a log rule as "a mathematical formula or table that gives an estimate of the net yield of lumber in board feet," with the diameter measured inside the bark at the small end, to the nearest inch:

Doyle is (D - 4)² × L ÷ 16, with D the small-end diameter in inches and L the length in feet, so an 8 ft log scales half the 16 ft figure: 32 board feet at 12 in. UT gives International 1/4-inch a formula for 4, 8, 12, 16, and 20 ft logs; for 8 ft, 0.398D² - 1.086D - 0.27 comes to 45 at 12 in after rounding to the nearest 5. The rules part ways on small logs: UT says Doyle "under-scales small logs and overscales large logs" and calls International 1/4-inch "the most accurate of the rules discussed," and in the table the two meet at 30 in. Doyle is "the most common rule used in hardwood log scaling in Tennessee," and Scribner Decimal C is common "on the West Coast and in the South for pine saw logs," so ask which rule a log buyer uses. The calculator above measures sawn boards, not logs.

Board feet, linear feet, and cubic feet

• Board feet to linear feet: linear ft per board foot = 12 ÷ (thickness × width): 2 for a 1x6, 1.5 for a 2x4, 1 for a 2x6.
• Linear feet to board feet: linear ft × thickness × width ÷ 12. 150 linear ft of 2x4 is 100 board feet.
• Board feet to cubic feet: divide by 12 (for softwood, a nominal volume).

Board feet to linear feet chart for common lumber sizes

1,500 linear ft of 2x4 make 1,000 board feet, or 1 MBF ("MBF is a thousand board feet," UT Extension). Linear ft = board feet × 12 ÷ (thickness × width), on the nominal size for softwood:

Hardwood works the same way with the quarter as the thickness: 4/4 x 6 in matches the 1x6 row and 8/4 x 6 in the 2x6 row. To turn linear feet into pieces, divide by the piece length: 1,500 linear ft of 2x4 is 187.5 pieces 8 ft long, so 188 pieces. The calculator also works backward: pick 2 in, enter 4 for the width, the total linear feet (150) as the length, and 1 board, and it shows "Total: 100 board feet."

Cubic feet to board feet (and cubic meters)

12 board feet make 1 cubic foot of lumber: a cubic foot is 1,728 cubic inches and a board foot is 144 (NIST Handbook 130). The last column is what a log of that solid volume saws out, from the UW fact sheet; metric figures in parentheses use NIST's factor for a cubic foot (0.02831685 m³):

The × 12 figure is board measure, so for softwood it counts the nominal size: 1,000 board feet of 2x4s is 83.33 cu ft nominal but 54.69 cu ft of wood at the actual 1 1/2 x 3 1/2 in. A log yields far less than 12 per cubic foot: UW says "we could obtain exactly 12 board feet from each cubic foot of solid wood" only without saw kerf, and puts typical Lake States trees sawn for lumber at "about 5-7 board feet per cubic foot." The calculator's cubic feet are its board feet ÷ 12, before any extra.

Tips and common mistakes

• Mixing nominal and actual. Enter 4 for a 2x4, not 3 1/2.
• Forgetting the quantity. The per-board figure is one piece; set the count.
• Length in inches. Length goes in feet: 30 in is 2.5 ft.
• Treating extra as a standard. It's your own allowance, applied to board feet only.
• Expecting the mill's exact tally. NHLA and Handbook 130 round surface measure to whole square feet; the calculator doesn't, so a mill tally can differ slightly.

Structural sizes: check your local code

This calculator measures volume only. Sizes and spans for joists, beams, posts, and headers come from your local building code (the deck calculator guide covers decks, and the stair calculator guide covers stair stringers); have structural framing checked by your building department or a qualified pro.