Board Foot Calculator

The board foot method is a standardized way to measure and value lumber (especially hardwoods). Because it measures volume rather than area or length, boards of different widths and thicknesses can be fairly compared. This calculator converts measurements into board feet, aggregates the amount of stacked lumber, and estimates cost and weight if desired. It can also be used to split up and calculate the value of a single log.

What is a Board Foot?

A board foot is a unit of volume equivalent to 144 cubic inches. Imagine a piece of lumber that is one foot long by one foot wide and one inch thick. That would be exactly one board foot. The shape doesn't matter, as long as the volume is the same. So a piece of wood with a thickness of two inches could still contain one board foot, even if only half of its surface area was one square foot.

It is important to distinguish three different units of measure: linear feet measures length only. Square feet measures area, or the product of length and width. Board feet measures volume, or the product of length, width, and thickness, and is therefore used in the lumber trade to price boards of varying dimensions.

How to Calculate Board Feet?

The formula for calculating board feet multiplies three dimensions and divides by 144 when all measurements are expressed in inches.

The length of wood is usually given in feet so the lengths are often quoted in feet and the number to divide by is referred to as 12.

Suppose you are buying five hardwood boards that each measure 8 feet long by 10 inches wide and 1.25 inches thick. The number of board feet in one board is calculated by multiplying 8 times 10, then multiplying the result by 1.25, and then dividing by 12, which gives you 8.33 board feet. For five boards, the total would be 41.67 board feet. If the price of lumber is $4.15 per board foot, then the total cost would be about $172.92.

This calculator allows you to pick any units you want. You can enter the thickness in millimeters, width in inches and length in feet. Because each measurement is converted separately then multiplied together, you will get an accurate board foot result no matter how you combine your units.

Common standards: number of board feet per lineal foot

For standard sizes the number of board feet is directly proportional to length. This table shows how many board feet are contained within each standard so that the total can be found by multiplying by the overall length.

When pricing by board feet length the nominal size and rough cut dimensions are used. The actual dimensions of a 2x4 after it is planed will be approximately 1.5x3.5 inches, but when calculating board foot lengths it is counted as a 2x4.

Estimation of the number of boards per tree.

A log is not simply processed into lumber. Some of the volume is lost in sawing operations, making boards and producing sawdust. Log rules determine how many board feet can be obtained from a single log, based on its diameter and length. The Doyle rule is most commonly used in the United States.

Here D is the diameter in inches measured at the thinner end inside bark and L is length in feet. A tree with a 10 inch diameter and 17 foot length would be estimated to yield about 38.25 board feet. The International 1/4 rule, which is built into the calculator, gives results that are closer to actual mill production. Smaller logs are estimated to have higher values than Doyle's Rule.

How much does the wood weigh?

Weight depends on the type of wood. By selecting a wood species in the "weight" section, a standard density for dry wood will be applied. Since a board foot is one twelfth of a cubic foot, weight is calculated by dividing the number of board feet by 12 and then multiplying by the density (pounds per cubic foot).

For example, oak weighs about 45 pounds per cubic foot when dry, so a board-foot of it would weigh approximately 3.75 pounds. Softwoods such as pine and spruce are much lighter, while hardwoods like hickory are denser and therefore heavier. Fresh lumber, or wood immediately after being harvested, is significantly heavier due to its high water content.

Tips when buying wood:

Don't just buy the bare minimum amount of wood. You'll need extra material to cut parts to size, match grain and color, and correct mistakes. It's a good idea to plan for about ten to fifteen percent more.

Hardwood lumber is graded in quarter inch increments. 4/4 means one inch, 8/4 means two inches. Sawmills calculate board feet based on this rough thickness and not the thinner dimensions after planing.

This calculator is for planning and estimating purposes only. As yields, prices and weights vary by supplier, species and moisture content you should check the quantity with a timber merchant before purchasing.