Board Foot Calculator
A board foot is 144 cubic inches of timber — one inch thick, twelve wide, a foot long. It is billed on the nominal size, not the size the board actually measures, which is where most of the confusion comes from.
Board feet
80.00board feet
- Board feet each
- 8.000
- Pieces
- 10
- Linear feet
- 80.0
- Cubic feet
- 6.67
- Cost
- $360.00
- A board foot is 144 cubic inches — one inch thick, twelve wide, a foot long. It is a measure of volume, so a 1x12 and a 2x6 of the same length are the same board foot.
- It is billed on the nominal size, not the planed one. A 2x4 measures 1.5 by 3.5 inches but is charged as two by four, so working from a tape measure undercounts the bill by about a third.
- Quarter measure is the other convention worth knowing: 4/4 is one inch, 5/4 is an inch and a quarter, 8/4 is two inches. It is thickness before planing.
About the board foot calculator
A board foot is a unit of volume rather than length or area, which is why a 1x12 and a 2x6 of the same length come to the same thing. It is 144 cubic inches: one inch thick, twelve inches wide, one foot long. Hardwood is sold by it almost everywhere, and construction lumber is often priced by it too.
The catch is that it is worked out on the nominal dimensions — the size the board was before it was planed. A 2x4 measures 1.5 by 3.5 inches after surfacing, but it is sold and billed as two by four. Working from a tape measure gives 3.5 board feet for an eight-foot 2x4 where the yard charges for 5.33, which is about a third out.
Hardwood adds its own convention on top. Thickness is quoted in quarters of an inch: 4/4 is one inch, 5/4 is an inch and a quarter, 8/4 is two inches. Those are rough thicknesses before surfacing, and a 4/4 board you actually receive is usually about 13/16 of an inch thick. You still pay for the full 4/4.
One thing worth knowing when the quote arrives: hardwood is often sold in random widths and lengths, so you buy a total board footage rather than specific boards. That means allowing extra for the cutting you will do to get the pieces you actually need out of what turns up.
What it works out
- Board feet for a single board or a whole order
- The cost at your own price per board foot
- Quarter measure — 4/4, 5/4, 8/4 and the rest
- Cubic feet, for shipping and drying calculations
The formula
Board feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12
The twelve is a unit conversion hiding in plain sight. A board foot is 144 cubic inches. Thickness and width are in inches and length is in feet, so multiplying them gives inch-inch-feet; dividing by twelve turns the feet into inches and the 144 into 1.
An eight-foot 2x6 is 2 times 6 times 8, divided by 12, which is 8 board feet. Ten of them is 80 board feet, and at four dollars fifty that is $360.
Because it measures volume rather than length, boards of different shapes come to the same figure. An eight-foot 1x12 is also 8 board feet — same volume, different proportions, same price.
Every one of those numbers is the nominal size. An eight-foot 2x4 is 5.33 board feet even though the board measures 1.5 by 3.5 inches and contains only 3.5 board feet of actual wood. The yard bills the nominal size, so that is what goes in.
- Thickness
- Nominal thickness in inches. In quarter measure, 4/4 is 1 inch and 8/4 is 2.
- Width
- Nominal width in inches — the name of the board, not what it measures.
- Length
- In feet.
- 12
- Turns inch-inch-foot into the 144 cubic inches of a board foot.
A worked example
Ten eight-foot 2x6 boards at four dollars fifty a board foot.
That works out to 80.00 board feet.
- Board feet each
- 8.000
- Pieces
- 10
- Linear feet
- 80.0
- Cubic feet
- 6.67
- Cost
- $360.00
Questions
What is a board foot?
144 cubic inches of timber — a piece one inch thick, twelve inches wide and a foot long. It measures volume, so a 1x12 and a 2x6 of the same length are the same number of board feet.
How many board feet is a 2x4?
5.33 for an eight-foot length: 2 times 4 times 8, divided by 12. That is worked out on the nominal size — the board itself measures 1.5 by 3.5 inches and holds only 3.5 board feet of wood, but the nominal figure is what you are billed for.
Why is a 2x4 not actually 2 by 4 inches?
It was, before it was dried and planed. The nominal size is the rough sawn size; the finished board loses about half an inch in each direction. The name stuck and the billing goes with the name.
What does 4/4 mean?
Four quarters of an inch — one inch of nominal thickness. It is how hardwood thickness is quoted: 5/4 is an inch and a quarter, 6/4 an inch and a half, 8/4 two inches. A surfaced 4/4 board usually arrives about 13/16 thick, and you pay for the full inch.
Is a board foot the same as a linear foot?
No. A linear foot is a length regardless of the board size — ten eight-foot boards are 80 linear feet whatever their section. A board foot includes the thickness and width, so those same ten boards could be 40 board feet or 160 depending on what they are.
How do I convert board feet to cubic feet?
Divide by twelve. A board foot is 144 cubic inches and a cubic foot is 1,728, so 80 board feet is 6.67 cubic feet. Useful for working out shipping weight or how much kiln space a load takes.
How much extra should I order?
Fifteen to twenty per cent on hardwood, more if you need particular figure or colour. Hardwood is usually sold in random widths and lengths, so you are buying a total footage and cutting your pieces out of whatever arrives — and knots, checks and sapwood all lose you material.
Why does the price per board foot vary so much?
Species and grade. Poplar and soft maple sit at the bottom, walnut and quarter sawn white oak near the top, and the difference between them is several times over rather than a few per cent. Grade matters as much — FAS boards yield far more usable wood than common grades, which is often worth the premium.