Whether you are a sawmill owner managing your land for sawlogs or you are interested in selling your timber and wondering how valuable a tree may be, it may be useful to know how to measure the board feet in a tree. Because board feet is a measurement of the yield of usable lumber a tree is likely to produce, the number of board feet in a tree is both a function of the size of the tree as well as the quality of its stem. As such, measuring board feet requires special measurements of the tree as well as specific knowledge about how to merchandize logs.
Don’t worry: We have you covered! In this article, we will discuss exactly how you can easily estimate the board feet of a tree using simple tools and calculations, and we will discuss the theory and assumptions behind these measurements. Before we begin, however, let’s understand exactly what the measurement of a board foot is.
What Is a Board Foot?
A board foot is defined as rough, green board measuring 12″x12″x1″. When we estimate the board feet in a tree (also called MBF for “thousand board feet”), we are measuring how many of these boards (or the equivalent volume) a tree can produce. However, when the logs are milled, there will be quite a bit of waste. The rounded slabs on the edge are not suitable for lumber and go to waste. Moreover, the kerf, or the material removed by the sawblade, also removes a fair amount of volume that is turned into sawdust. On top of the inherent wastes in a given log, any tree will also have a great deal of material that is unusable as a log, either due to size, sweep, or other defects.
Because of these considerations, measuring board feet in a tree or log is extremely different from measuring cords or other units of gross volume. With that in mind, let’s discuss how to measure the board feet of a tree.
Measuring the Board Feet in a Tree
To measure the board foot volume of a tree, we need to find two pieces of data:
- Diameter (or “DBH”)
- Merchantable Height (by number of 16-foot logs)
With those two data, points, we can use what is known as a log rule to determine the likely board foot yield of that tree. Below is a table of the International 1/4-inch log rule.
This is not the only log rule available, however. There is also The Doyle rule and Scribner rule. These rules can be more common out in the Midwest and West, but because they do not calculate allowances for log taper, they are widely considered to be less accurate. The international rule tends to be the most common overall, and it is standard with most forest service agencies.
Now let’s dig into how to use this table.
Finding Tree Diameter
The first step to using the log rule table above to estimate board feet is finding the tree diameter. To do this, you can either use a D-tape, a flexible measuring tape, or even a rope. You can also use a tool known as a tree and log scale stick, but we’ll go over the use of that device in more detail later.
However, regardless of how you measure, it important to understand what is meant by “DBH.” DBH, or Diameter Breast Height, is a standard definition of tree diameter, and it refers to the diameter of the tree exactly 4.5′ off the ground.
If you want more detail on exactly how to take that measurement, we have an entire article (and video) on the topic here. Yes, it is nuanced enough that it really deserves its own article. I recommend you give it a read.
Determining and Measuring Merchantable Height (Number of Merchantable Logs)
The second and arguably most important step in finding the board feet in a tree is determining and measuring the merchantable height. Merchantable height is the total height of the tree that can be used as a sawlogs. In other words, if a tree forks or otherwise becomes poor quality 32 feet up, the tree only has 2 merchantable sawlogs, even if It can be used as pulpwood for another 20 feet. Below is an example of where the merchantable height might end on two different trees.
In the case of these trees, the one on the left is excessively branchy, and so it only produces one small usable log near its base. Above that is pulpwood, which cannot be used for lumber. To the right, however, the stem is straight and clean, so it has a great deal of merchantable volume. Other defects that might affect merchantable height are forks, sweeps, scars, and of course rot.
The defects that affect merchantable height will depend on the species you are merchandizing, however. Branches and knots don’t matter much for softwoods, which generally produce structural lumber, but they are extremely important for hardwoods, the wood of which is often used for cosmetic surfaces. Thus it is important for you to know the specifications of logs for your local mill (or your personal limits if you are milling yourself) to accurately measure the board feet in a tree.
Once you have a decent idea of where the cutoff for merchantable height should be, you must be able to find that height. Luckily, we have a great article here on the subject. Use the method outlined there, but instead of measuring to the top of the tree, measure to the merchantable height.
When measuring, it is also a good idea to assume a one-foot stump height. Simply deduct that from the merchantable height.
Using a Tree and Log Scale Stick to Measure Board Feet
A great alternative (or rather two-in-one tool) to the above is using a Tree and Log Scale Stick. A tree and log scale stick has pre-measured markings for log heights, diameter, and even log rule tables themselves! These handy tools make the process of estimating board feet substantially easier. Here is how you use one:
Step 1: Take Position and Sight-in the Tree
The first step is to stand 66′ from the base of the tree, and hold out the stick 25″ from your eye, as seen below:
Step Two: Determine the Number of Logs
Holding it from this position, you can see markings on the right side of the stick indicating the number of logs. If you are standing 66′ from the tree as you are supposed to, these markings indicate individual 16′ lengths. Determine how much of the tree is usable as sawtimber and use these marking to determine how many usable logs can be obtained from that length. Be sure to account for stump height!
Step 3: Find Diameter
The tree and log scale stick stick also comes with markings that you can use to visually measure diameter. Same rules apply as before: measure 4.5 feet off the ground, but this time, the tool must also be held 25 inches from your eye. At this distance and height, the markings can measure diameter accurately.
Step 4: Find the Board Feet
Using the diameter and number of logs, you can find the board feet using the 1/4″ International log rules printed on the stick. In this case, we have an 11″ diameter and 2 logs, which gives us 75 board feet!
Unfortunately, the log rule table printed on the tree and log scale stick stick only measures to whole 16′ lengths, but using the table above in this article, you can estimate to 8′ lengths as well.
Finding the board feet within a tree can be more art than science. It involves a lot of assumptions and estimations that may not hold true. Moreover, learning how to properly deduct for defect and accurately determine how many logs a tree can actually produce can take a lot of practice, study, and experience. Regardless, with the skills and info provided in this article, you are ready to go out and start gaining that experience, so what are you waiting for? Get out and start scaling!
If you want to learn more about forest measurements and managing your woodlands, grab a copy of our free guide with the link below: