Board Feet Calculator
Convert thickness, width, length, and piece count into board feet using the standard lumber tally.
Total board feet
5.33 bd ft
What is a board foot?
A board foot is the North American unit of lumber volume. One board foot equals a piece 1 inch thick, 12 inches wide, and 12 inches (1 foot) long: 144 cubic inches of nominal wood. Any board that adds up to 144 cubic inches is one board foot, so a 1x12 that runs 1 foot and a 1x6 that runs 2 feet are both a single board foot.
The unit exists so wood of different widths and lengths can be priced and tallied on one scale. A lumberyard, sawmill, or hardwood dealer that sells by volume quotes board feet, or thousand board feet (MBF) for wholesale loads. Dimensional framing lumber at a home center is usually sold by the stick, but rough hardwood, cedar, and most mill-direct stock are still counted in board feet.
The one trap is nominal versus actual size. Board measure is calculated from the nominal size stamped on the board (the “2x4”), not the smaller dressed size a tape shows (about 1.5 by 3.5 inches). Get that distinction right and the rest is arithmetic.
How to calculate board feet
Formula
board feet = (thickness in × width in × length ft × quantity) ÷ 12
How the formula works
Board feet = (thickness in inches x width in inches x length in feet x quantity) / 12. The divide-by-12 is a unit conversion, not a fudge factor. Thickness and width are in inches and length is in feet, so the raw product is in inch-inch-feet. One board foot is 1 inch by 12 inches by 1 foot, so dividing by 12 turns the width from inches into feet and leaves the answer in board feet. If every dimension is in inches instead, divide by 144; both routes describe the same 144 cubic inches. This matches DOC PS 20, which states board measure as nominal thickness in inches times nominal width in feet times length in feet.
Which size to enter
- For standard dressed softwood, enter the nominal size on the grade stamp (2x4), not the dressed size (1.5 by 3.5 inches). Board measure in the American Softwood Lumber Standard is defined on nominal thickness and width.
- Hardwood sold in quarters maps to rough thickness: 4/4 is 1 inch, 5/4 is 1.25 inches, 8/4 is 2 inches. Enter the rough thickness; surfaced hardwood finishes thinner.
- If you are milling custom stock or want the true rectangular volume of a surfaced board, enter the measured thickness and width and note that basis on your cut list.
- The Forest Products Laboratory notes stock under 1 inch nominal is commonly tallied as 1 inch. This tool does not auto-round thin stock, so enter 1 inch if you want that convention.
Rounding and invoices
The live figure is the exact formula result; the display shows up to two decimals, which is standard for a DIY tally. Cubic inches are shown alongside so the 144-cubic-inch relationship stays visible. A yard invoice can differ because sellers group random lengths, tally rough versus dressed size differently, or round at the line-item or order level. Use this page to check the math, then reconcile against the seller’s stated basis. MBF means 1,000 board feet.
Example
- 1Thickness × width × length2 in × 4 in × 8 ft = 64
- 2Divide by 1264 ÷ 12 = 5.33 bd ft per piece
- 3Multiply by quantity5.33 × 1 = 5.33 bd ft total
FAQ
Practical answers for the board-foot tally used at yards and mills.
What is a board foot?
A board foot is a volume unit, not a stick of lumber sitting on a rack. The USDA Forest Products Laboratory defines it as a board 12 inches long, 12 inches wide, and 1 inch thick, or any other shape with the same 144 cubic inches of volume. A 1 x 12 that is 1 foot long is 1 board foot. A 1 x 6 that is 8 feet long is 4 board feet.
Should I use nominal size or the actual dressed size?
For buying standard softwood, use the nominal size: a 2x4 is tallied as 2 inches by 4 inches even though dry dressed stock is typically 1.5 inches by 3.5 inches. DOC PS 20 says board measure uses nominal thickness and width, while cubic measure uses dressed sizes. If you are milling custom stock or measuring a board with a tape and want the true rectangular volume, enter the measured thickness and width instead, and say so on your cut list.
Do I enter length in feet or inches?
Either. The industry formula wants length in feet. If you have a tape reading in inches (96 in for an 8 ft 2x4), switch the length unit to inches. The calculator converts inches to feet by dividing by 12, then applies (T x W x L_ft) / 12. Mixed feet-and-inches (8 ft 6 in) should be converted to 8.5 ft or 102 in before you enter them.
How do hardwood quarters (4/4, 5/4, 8/4) map to thickness?
Hardwood is often sold in quarter-inch rough thickness: 4/4 is 1 inch, 5/4 is 1.25 inches, 8/4 is 2 inches. Enter that nominal rough thickness in inches. Surfaced hardwood will be thinner than the quarter size. NHLA rules govern hardwood inspection and tally at the mill; this calculator does not apply grade deductions or random-length grouping. Confirm how your dealer tallies surfaced vs rough stock.
Why does the formula divide by 12?
Thickness and width are in inches; length is in feet. One board foot is 1 in x 12 in x 1 ft. Multiplying thickness (in) by width (in) by length (ft) gives inch-inch-feet. Dividing by 12 converts the width from inches into feet so the product is board feet. If every dimension is in inches, divide by 144 instead; both paths equal 144 cubic inches per board foot.
What is MBF, and will this match my invoice?
MBF means 1,000 board feet, a common wholesale unit. A yard invoice may also list piece count, nominal size, and length. PS 20 notes that invoices for dressed lumber of standard sizes should show the number of pieces of each nominal size and length as well as the actual thickness and width. Small differences can come from rounding, how lengths are grouped, or whether the seller tallied rough vs dressed size. Use this page to check the math, then match the seller's stated basis.
Sources
1. Voluntary Product Standard PS 20-25, American Softwood Lumber Standard
U.S. Department of Commerce / NIST
Section 2.2 defines board measure: board feet = nominal thickness (inches) x nominal width (feet) x length (feet). Section 4 covers tally of standard and nonstandard sizes.
https://www.nist.gov/system/files/documents/2024/12/11/PS%2020-25%20Final.pdf2. Voluntary Product Standards Program
National Institute of Standards and Technology
NIST administers DOC Voluntary Product Standards, including the current American Softwood Lumber Standard (PS 20-25).
https://www.nist.gov/standardsgov/voluntary-product-standards-program3. Wood Handbook: Wood as an Engineering Material (FPL-GTR-190), Glossary
USDA Forest Service, Forest Products Laboratory
Defines a board foot as a board 12 in long, 12 in wide, and 1 in thick (or cubic equivalent), with practice based on nominal thickness and width and actual length.
https://www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr190/glossary.pdf4. Wood Handbook, Chapter 5: Commercial Lumber
USDA Forest Service, Forest Products Laboratory
Covers nominal vs dressed sizes for yard and structural lumber and reminds buyers that board measure depends on the thickness and width nomenclature used.
https://www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr113/ch05.pdf
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