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 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, 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).

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.