A board foot is a unit of volume used for rough and hardwood lumber: one hundred and forty four cubic inches, which is a board one inch thick, twelve inches wide and one foot long. It exists because rough lumber is sold by volume rather than by the piece, and it confuses people because the nominal size a board is called is not the size it measures after planing. Both facts matter when you are converting a cutting list into an order.
The board feet calculator arithmetic, in one line
Thickness in inches multiplied by width in inches multiplied by length in feet, divided by twelve, gives board feet. For a list of boards, do each and add them. That is the whole calculation, and every board foot calculator is a wrapper around it.
Nominal against actual: the carpenter calculator conversion that trips people up
A board called two by four measures less than that after planing, and hardwood is sold in quarter-inch thickness steps of the rough dimension. Use the nominal size when the supplier prices by it, and the actual size when you are working out whether your cutting list fits. Mixing them is the usual source of a short order.
From board feet to the boards you can actually buy
Lumber comes in stock lengths, so a board footage total is not yet an order. Work out how many pieces of each length your cutting list needs, allowing for the cuts you cannot avoid, and then convert to board feet for pricing. Answering how many boards do i need in pieces is what the yard can fill.
Questions people ask about board foot calculator
Is a board foot a measure of volume or of area?
Volume. It is often confused with a square foot of surface because the reference board is one inch thick, which makes the two numerically equal at that thickness and different at any other.
Why is my two by four not two inches by four inches?
Because the nominal name refers to the rough sawn size before drying and planing. Softwood dimensional lumber is sold by the nominal name at the actual finished size, and every carpenter learns the difference early.
How do I price hardwood by the board foot?
Calculate the board feet of the rough boards you need, including the waste from cutting to your finished sizes, and price at the yard's rate for that species, grade and thickness. Pricing on finished dimensions alone will always come up short.