The Four Timber Measurement Units You Need to Know

Timber truly is one of the most ancient industries around. We have been harvesting and utilizing wood for energy and construction for millennia, but only recently has forestry itself become an established science and practice. Like any science, measurement is key to successful timber management, but that’s where the simplicity ends. Timber measurement units are anything but standardized, with different regions, species, and product classes using different units that describe entirely different things. The four main timber measurement units used are cords, tons, board feet, and cubic feet. In this article, we will tell you everything you need to know about these four major measurement units and their differences, strengths, and weaknesses.

1. Cords

A cord is a standard unit of measurement for firewood, pulpwood, and other small-diameter roundwood. The measurement of a cord is 128 cubic feet or 3.62 cubic meters. It is a volume measurement that is equal to a stacked pile of wood that is 8 feet long, 4 feet wide, and 4 feet high. The wood must be stacked in a neat, compact pile, with the pieces lined up parallel to each other and tightly packed. Even then, however, the measurement still includes air gaps between the pieces of wood.

Cords are a bit of an outdated unit. It used to be standard in the pulp and paper industry when only volume mattered and it was impractical (if not impossible) to measure by weight. These days, mills are equipped with precision scales to measure incoming trucks, allowing sales to be conducted on the basis of weight. Cords are still used, but they are used almost exclusively for firewood or small, informal sales of logs.

2. Tons

Tons are a weight measurement used for pulpwood, wood chips, and even sawtimber not sold on the basis of quality (such as spruce and fir). A ton of wood is equal to 2,000 pounds or 907 kg. Unlike cords, which are a measurement of volume, tons measures the mass of the wood, so equivalent volume can have more or less weight depending on species. Hardwoods like maple, oak, and hickory tend to be heavier per cord than softwoods like spruce, fir, and pine, which is a major difference between those measurements. A cord of hardwood usually weighs around 2.75 tons, while a cord of softwood weighs 2.35 tons.

While tons are a standard measurement for many forest product classes, and it is arguably the most objective of the four, it still comes with inherent problems, namely that it mostly measures water. A bulk of a tree’s weight is the moisture content inside the wood, but this weight is both variable and unwanted. For example, a tree’s moisture content during a drought will likely be lower than during the rainy season, so if these trees are sold on the basis of weight, they are technically worth less. Even more paradoxically, the drier trees are more valuable to the mill. boards must be kiln dried before being sold to the consumer, and this kiln drying process is energy intensive and expensive. When trees are dryer, they need less time in the kiln. On the other hand, the bark of trees can hold a lot of ice and snow in the winter, so mills end up paying for snow instead of wood.

3. Board Feet

Board feet (also abbreviated MBF for thousand board feet) is a measurement used to determine the volume of sawn lumber. It is a unit of volume equal to a green, unplaned board measuring one foot long, one foot wide, and one inch thick. A board foot is equal to 144 cubic inches or 2,359 cubic cm of wood. You can see a real example of this hypothetical unit below.

Unlike cords, which are a unit of measurement, and tons, which are a measurement of weight, board feet are a measurement of yield. Measuring the board feet of a tree is an attempt to estimate the actual amount of lumber that can be sawn from its logs. This inherently makes board feet a more complicated measurement, as it attempts to judge the actual economic utility of a log.

While the definition of a board foot is standard, the measurement process is far from it. To measure board feet, the timber industry uses a set of formulas known as “log rules” to estimate its yield. There are three primary log rules used: The international 1/4″ rule, the Doyle rule, and the Scribner rule.

The international 1/4″ rule assumes a 1/4″ kerf and a certain amount of taper in the stem. The Doyle rule is used for larger timber, has no taper assumption, and tends to under-estimate smaller timber. The Scribner rule is different in that it isn’t based on a formula, but rather a series of milling diagrams that estimate the yield of hypothetical logs. Other log rules exist, but they tend to be proprietary or regionally-focused, such as the Maine rule.

Unfortunately, measuring board feet is a complicated and skillful process, usually requiring the assistance and judgement of trained scaling professionals. It is also time consuming, as logs must be measured individually opposed to measuring an entire truckload at a time, as is the standard with cords and tons. Thus, it is usually reserved for valuable sawlogs were basing value on the quality of the log is essential.

4. Cubic Feet

Cubic feet is a measurement of the volume of wood, similar to cords. However, unlike cords, it refers only to the solid wood volume of the timber. In this sense, it is an attempt to measure the economic utility of logs based on volume, similar to board feet. A cubic foot is equal to a piece of wood that is 1 foot long, 1 foot wide, and 1 foot thick.

While this unit is used for conducting commerce in the industry in certain jurisdictions, it isn’t incredibly common (Although cubic meters are standard in some parts of the world). Arguably, the primary use of cubic feet is for measuring growth. It is a relatively objective way to express volume growth per year, so it isn’t uncommon to see it used in inventory and growth reports for a land base.

Timber Measurement Units Can Be Confusing, But They Are Necessary