Board Foot Calculator
Calculate lumber board feet from thickness, width, length, and quantity. Useful for pricing wood, planning cuts, and ordering materials.
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What the board foot calculator does
Hardwood is sold by the board foot, a measure of volume, so a pile of boards in different sizes all comes down to one figure for pricing and ordering. This works it out. You enter each board's thickness, width, length, and quantity, and it returns the board feet and a cost, adding as many different boards as your project needs.
It turns a cut list into a lumber order. Below is how it works and the one convention that trips everyone up.
How to use it
- Enter the first board's thickness, width, and length, each with its unit, and how many of that board you need.
- Add a price per board foot if you want a cost.
- Use Add Board for each different size in your project, then press Calculate, or Reset to clear it.
How board feet are worked out
Board feet measure the volume of wood, so the calculation multiplies the three dimensions together and scales them to the standard unit:
Board feet = (thickness × width × length in inches) ÷ 144, times the quantity
The 144 is there because a board foot is 144 cubic inches, which the next section explains. The calculator works out each board, multiplies by how many you need, and adds them all up, with a running cost if you have entered a price.
What a board foot is
A board foot is a unit of volume, not area, which is the thing to hold onto. One board foot is a piece of wood a foot long, a foot wide, and an inch thick, which works out to 144 cubic inches. That is the whole definition, and every board foot calculation comes back to it.
Because it measures volume, it captures thickness in a way that length alone cannot. A long thin board and a short thick one can hold the same amount of wood, and the board foot counts both fairly, which is why lumber yards price by it rather than by the running length. A thicker board costs more for the same face size, and board feet are why.
Nominal versus actual size
This is the convention that costs people money when they do not know it. Lumber is often called by a nominal size, the size before it was dried and planed, which is larger than the actual size you measure. A construction two by four is really about one and a half by three and a half inches once it is surfaced.
For hardwood, board feet are figured on the nominal, rough-sawn thickness, the size before surfacing, not the smaller finished measurement. Hardwood thickness is quoted in quarters of an inch for this reason: four-quarter, written 4/4, means one inch rough, and eight-quarter, 8/4, means two inches. So you pay for the inch even if the planed board measures less. The practical rule is to enter the dimensions your supplier prices by, and to confirm which those are, since using the wrong ones throws the figure off.
A worked example: a 1 by 6 board
Say you need a board 1 inch thick, 6 inches wide, and 8 feet long.
Eight feet is 96 inches, so that is (1 × 6 × 96) ÷ 144 = 4 board feet. For four of them, the total is 16 board feet, and a price per board foot gives the cost.
A construction two by four eight feet long is the example to watch: by its nominal 2 by 4 it is 5.33 board feet, but by its actual 1.5 by 3.5 inches it is 3.5, which is exactly why it pays to know which size your supplier means.
Questions people ask
How do I calculate board feet?
Multiply thickness, width, and length in inches and divide by 144, then multiply by the quantity. A 1 inch by 6 inch by 8 foot board is 4 board feet.
What is a board foot?
A unit of lumber volume equal to 144 cubic inches, a piece a foot long, a foot wide, and an inch thick.
Do I use nominal or actual dimensions?
Hardwood board feet are figured on the nominal, rough-sawn size. Confirm which dimensions your supplier prices by, since the difference changes the total.
What does 4/4 mean for lumber?
It is hardwood thickness in quarters of an inch, so 4/4 is one inch rough, 8/4 is two inches, and so on.
References
A quick note on the numbers. The board foot, 144 cubic inches, and the rules for figuring it on nominal rough-sawn dimensions are the standard set by the National Hardwood Lumber Association. The calculation itself is plain geometry, the three dimensions multiplied and scaled. The unit conversions follow the US National Institute of Standards and Technology guide.
- National Hardwood Lumber Association (NHLA), board foot measurement and grading rules. https://www.nhla.com
- National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811
Mahendra Thapaliya is a graduate student in Structural Engineering at the University of Bologna, with research interests in structural systems, FEM, earthquake engineering, and numerical modeling. At Eon Tools, he reviews construction tools.