How Do You Calculate a Board Foot?

A Board Foot is an Important Measure Used in the Logging Industry

Finland Sawmill
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If you are in the logging or lumber industry, you may receive calls from customers who have recently cut down a tree and want to have it milled. The cost is usually dependent on how many board feet will be produced after milling, but when asked how big the tree is, most customers respond with things like "I can't get my arms around it." While it's understandable that's how they would measure it, it's far too vague to be of use to a logger.

  There are far more accurate ways to determine how many board feet are in a log. 

Board Foot and the Doyle Log Scale

A board foot is 12" x 12" x 1". It is a specific unit of measure used in the United States and Canada for the volume of lumber. It is often abbreviated as FBM (Foot, Board, Measure). 

To estimate how many board feet in our log, there are a variety of scales that have been created. The Doyle scale is one of the most commonly used formulas for calculating board feet. Developed in the 1800's, it is based on a mathematical formula and is most prominently used in the South and Midwest United States. The Doyle scale is the standard by which hardwood lumber is bought and sold. 

It estimates large or medium logs very close to the actual number but underestimates in smaller logs. Because it comes in below the price, this is the scale most log buyers want to use. 

Log buyers typically keep a Doyle scale with them.

It looks like a folding ruler with the footage labeled at each inch marker. 

The Doyle scale formula is based upon a tapered cylinder. Straight legs without minimal tapering will produce more board feet than the scale estimates but it typically balances out since most logs are imperfect.

To estimate the board feet from a log, measure the average diameter of the smaller part of the log in inches.

Then, measure the length of the log in feet. Move the scale's marker over to where these two measurements meet. Where the two measurements intersect is the approximate board foot output. If there are any defects, you can reduce the number based on how significant that flaws are, such as rot or curvatures. 

Sawmills charge by the board foot, so the scale can help determine what the cost will be. It's essential to accurately measure the log, rather than guessing at its diameter. Most people are way off when guessing a log's size. 

The Doyle scale is a valuable tool for professionals working in the logging and lumber industries. Whether you are removing trees for a neighbor or purchasing wood to mill, the amount of board feet is what determines the cost. While the Doyle scale can be inconsistent, particularly for smaller logs, it can give you a ballpark estimate of how many board feet are in a log, so you have an idea of what the final cost will be. This can prevent any surprises for you and the miller handling the log.