Measuring Wood Volumes

Illustrations by Joseph Smith

An important skill for any woodland owner who is preparing to sell some wood is understanding how wood volumes are measured. There are ways to measure live wood “on the stump” that are useful for preparing forest management plans, but in this column, we’ll be concerned with measuring the volume of cut wood that is ready to enter the market.

Many of us are familiar with the way firewood is measured – as cords. A cord of firewood represents a 4-foot-high by 4-foot-wide by 8-foot-long pile of stacked firewood, or 128 cubic feet of wood with allowance for the air space between the pieces of stacked wood. It is not a precise measurement, but for a lower-value product like firewood, it is good enough. Two other wood products of lower value are chips, which are used for power generation, and pulpwood, used for making paper. Chips are priced by the ton, and pulpwood by the cord.

Sawlogs have a much higher value than firewood and are measured more precisely. The process of measuring the volume of wood in a sawlog or pile of sawlogs is known as scaling. Sawlogs are measured by the board foot, which is a solid volume of wood one inch thick by one foot wide by one foot long – it sounds like what it is. A true 2x6 that’s 12 inches long, and a 1x6 board 2 feet long each contain exactly one board foot of wood.

To determine the number of board feet in a log, scalers use a rule, a piece of wood that looks somewhat like a yardstick, but which, to the uninitiated, has a puzzling array of numbers on each side. As a result of history and strongly held opinions, there are a number of different rules in use – the Scribner, Doyle, and the International ¼-inch rule are used in different parts of the Northeast, with the latter the most widely used. The different rules use different parameters for determining the number of board feet in a log, and each has a chart so a scaler can plug in the diameter and length of the log to get the number of board feet, conveniently avoiding the need for a mathematical volume calculation on each log.

Let’s go through the process of scaling a maple log. Imagine you have a 16-foot-long maple log that measures 17 inches in diameter inside the bark at the small end. Using the International ¼-inch Rule, this log, without any obvious defects, such as a hollow center or a void elsewhere, would scale at 205 board feet. Another way to express that is .205 thousand board feet or .205 MBF.

One thousand board feet is an important measurement because sawlog prices are generally expressed per thousand board feet, or per MBF. Those prices represent what a mill would pay for a thousand board feet of a certain species and grade of log, delivered to the mill. Veneer logs are also paid for by the thousand, and because they need to meet very stringent specifications the price per thousand is much higher.

 

Carl Demrow is a trail consultant and carpenter when he’s not busy tending his woodlot in Washington, Vermont.

 
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