Board feet trip up almost everyone who buys hardwood for the first time - and plenty of experienced buyers too. It is not a measure of length, and it is not the same as a cubic foot. Get it wrong and you can over- or under-order by a wide margin. This guide makes it simple.
What a board foot actually is
A board foot is a unit of volume used for hardwood lumber, mostly in North America and widely in the Indian hardwood trade. One board foot equals a piece of wood 12 inches long, 12 inches wide and 1 inch thick - in other words, 144 cubic inches of timber.
The key insight: a board foot is about volume, so the same board foot can take many shapes. A board 1 inch thick must be a foot square to make one board foot; a board 2 inches thick only needs to be half as long. It is the cubic content that counts, not any single dimension.
The formula
The standard board-foot formula, using inches for thickness and width and feet for length, is:
Board feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12
The divide-by-12 converts the mixed units into the 144-cubic-inch board foot. If you prefer everything in inches, divide by 144 instead:
Board feet = (Thickness × Width × Length, all in inches) ÷ 144
A worked example
Say you have a board 2 inches thick, 8 inches wide and 10 feet long:
- Board feet = (2 × 8 × 10) ÷ 12
- = 160 ÷ 12
- = 13.33 board feet
For ten identical boards, that is 133.3 board feet. At a price of, say, a given rate per board foot, you now have a true volume to cost against.
The mistakes that cost money
They are not the same. One cubic foot equals 12 board feet, because a cubic foot is 12 inches thick where a board foot is only 1 inch thick. A price quoted per board foot looks far cheaper than the same wood quoted per cubic foot - always confirm the unit before comparing suppliers.
Rough-sawn lumber is measured at its full rough dimension, but planed (surfaced) lumber loses material. A "1 inch" board often finishes at 3/4 inch. Know whether you are paying for nominal or actual volume.
Board footage is gross volume. It says nothing about how much usable, clear timber you will recover after cutting around knots and splits. For that, you need to think about yield and grade.
How it relates to CFT and cubic metres
If you trade internationally, you will meet several volume units. Here is how they line up:
| Unit | Equals | Common use |
|---|---|---|
| 1 board foot | 144 cubic inches | US & Indian hardwood lumber |
| 1 cubic foot (CFT) | 12 board feet | Indian timber markets |
| 1 cubic metre | ~423.8 board feet | International contracts |
| 1 cubic metre | ~35.31 cubic feet | International / metric |
The takeaway
Board feet measure volume, not length, and one board foot is 144 cubic inches. Memorise the formula - thickness times width in inches, times length in feet, divided by twelve - and always check whether a price is quoted per board foot, per cubic foot or per cubic metre before you compare it. Those three units differ by factors of twelve and thirty-five, so a unit mix-up is one of the most expensive mistakes in timber buying.