The lumber calculator converts a board's thickness, width, length and piece count into board feet, the unit hardwood dealers and sawmills price by. Framing lumber at a home center is sold by the piece, so for a deck or a fence this page is a way to compare stock, not a way to buy it.
The one thing to get right is the difference between nominal and actual dimensions. A 2×6 is not two inches by six inches, and the calculator expects the real number.
How to use it
- 01
Enter the actual thickness and width in inches
Surfaced dimensional lumber is smaller than its name: a 1× board is ¾ inch thick, a 2× is 1½ inches, a 4× is 3½ inches; widths run 3½ for a ×4, 5½ for a ×6, 7¼ for a ×8, 9¼ for a ×10 and 11¼ for a ×12. Rough-sawn hardwood is the exception — it is sold by its nominal quarter thickness, so enter 4/4 as 1 inch.
- 02
Enter the length in feet and the piece count
Length is in feet, not inches. Run the calculator once per size in your cut list rather than averaging; board feet do not add correctly across mixed sizes unless each is computed on its own.
How the math works
The formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12, times the number of pieces. A board foot is 144 cubic inches — a piece one inch thick, twelve inches wide and one foot long. A 2×6 eight feet long entered as 1.5 × 5.5 × 8 is 5.5 board feet; twelve of them are 66.
Why nominal sizes overstate the count
Entering a 2×6 as 2 × 6 instead of 1.5 × 5.5 inflates the result by 45 percent. For a dealer selling surfaced stock by the board foot, that is the difference between the price you expect and the one on the invoice.
What it does not do
It has no waste factor and no kerf. A cut list that yields four 24-inch pieces from an 8-foot board is not quite four pieces once the saw blade is counted; add a piece or two for anything cut to length.
Where the number goes wrong
- Using nominal dimensions for surfaced lumber. The calculator wants 1.5 and 5.5, not 2 and 6.
- Confusing board feet with linear feet. Linear feet ignore width and thickness; a lumber list in linear feet only works for one size at a time.
- Entering length in inches. An 8-foot board entered as 96 gives a number twelve times too large.
- Forgetting that pressure-treated lumber is often wetter and slightly larger fresh from the store; measured dimensions can differ from the table until it dries.
Questions people ask
How many board feet are in a 2×4 that is 8 feet long?
3.5. The actual size is 1.5 by 3.5 inches, so 1.5 × 3.5 × 8 ÷ 12 = 3.5 board feet.
What is a board foot?
A volume: 144 cubic inches, the same as a board one inch thick, twelve inches wide and one foot long. Hardwood, rough-sawn stock and many specialty woods are priced per board foot.
Is framing lumber sold by the board foot?
Usually not at retail — a home center prices a 2×6×8 as one item. Sawmills, hardwood dealers and bulk orders use board feet, and that is where this calculator earns its keep.