Proper estimation of volume is an integral part of forest management, and when forestry is done on a small scale, it can help to look at volume on a per tree basis instead of a larger per acre basis. So how many cords of wood are in a tree? Obviously, the number varies drastically, but a good rule of thumb is that a tree with a diameter of 12 inches and height of 50′ will have .25 cords of wood total. Below is a volume table you can use to estimate the volume of individual trees:
How to Use This Volume Table
To determine the number of cords in a tree, you need two things:
- Diameter at Breast Height (DBH)
- Total Tree Height
To find the diameter at breast height, use a specialized diameter tape to measure the diameter at 4.5′ off the ground. Alternatively, you can measure the circumference of the tree at 4.5′ with a normal measuring tape and divide the circumference by 3.14 to get the diameter. For more detail on how to measure tree diameter, read our article here. To find the height, however, you will need to either cut the tree down and measure it on the ground, use trigonometry, or estimate with your best judgement. Using trigonometry is your best option if you want an accurate answer. Unfortunately, that can take specialized tools and complicated math, but there is an easy way to do it if you are short on time and resources (and math skills).
Quickly Measuring Tree Heights for a Volume Estimate.
The easiest way to to take a quick measurement of tree height while it is standing is to find a stick and use it to calculate some quick trigonometry. Here is how:
- Find a stick that is the same length as the distance between your hand and your eye when your hand is held at eye level.
- Stand back, hold the stick at a 90 degree angle and level with your eyes, and begin walking toward the tree.
- Once the top of the stick is visually aligned with the top of the tree, stop.
- The distance between you and the tree is now equal to the tree’s height.
- Now, simply measure the distance with a 100′ tape or pacing, and you will have a decently accurate measurement of the tree height.
Limitations of the Cords Per Tree Volume Table
This table provides only an estimate of the amount of cords of wood in a tree. It does come with certain limitations. First, It is designed only for estimating hardwood volume. It is not accurate for softwoods (which are often not measured in cords). Additionally, the original data is taken from New York State, so it may not be as accurate in other areas. It is based on a combination of several hardwood species, so the volumes for individual species may differ due to weight and size differences. Nonetheless, this table can be a useful way to estimate volumes, especially for firewood harvest management.
What Affects the Wood Volume of a Tree?
Trees come in all shapes and sizes, so tables like the one provided can only use averages to estimate individual volumes. The factors that affect the number of cords in individual trees, however, are numerous. Here are a few of the biggest factors:
Height and Diameter Ratios
The two largest factors contributing to volume are of course height and diameter, which is why these two numbers are usually how volume is estimated. However, a tree’s ratio between height and diameter are not consistent. Trees grown more in the open tend to have more diameter relative to height, and trees grown in dense environments tend to be taller and have smaller diameters. Similarly, as a tree grows older, it will stop growing in height and grow only in diameter, affecting that ratio greatly. To learn more about how trees grow in regards to height and diameter, we have a discussion of the topic here.
Taper
Trees that are grown in the open have another problem: taper. In order to move their center of mass downward to increase stability, the diameter of an open-grown tree tapers substantially as it grows taller. This taper can potentially have a sizable impact on total volume, and it may noticeably reduce the amount of cords of wood in a tree.
Rot
Often, fungus causes trees to rot and decompose while they are still standing. In some cases, The tree can be rotting away faster than new growth is adding volume! Unfortunately, it can be difficult to see rot from the outside, so while a larger tree in theory may have .75 cords of wood inside, you may cut it down to see it has substantial rot, and it only yields .5 usable cords.
Crown Volume
In most cases, the crowns of a tree are a relatively negligible part of its volume, but in some species, and particularly in open-grown trees, the limbs of a tree can be thick and represent a substantial amount of volume. Because of the variability of crowns, however, estimating the number of cords in a crown is incredibly difficult. In any case, if you are looking at a tree with a large crown and thick limbs, it is possible you may underestimate total volume.
A Single Tree Can Hold A Surprising Amount of Wood
A cord may seem like a lot of wood, but it doesn’t take all too many trees to reach that volume. In truth it only takes about four decently sized trees to equal a cord of wood. If a home is burning 5 cords of wood a year, that means they are burning about 20 trees a year. Considering a single acre can hold hundreds of trees, and the average acre of forest in the US grows about .6 cords per acre per year, you can quickly see how managing a woodlot for firewood production can be one of the most sustainable methods of heating your home available. Next time you are out on your woodlot or in a forest, bring a notepad and a tape measure and use the table provided here to estimate the cords of wood in trees you see. You may be surprised how quickly it adds up.