How to Measure Tree Diameter with Household Items or Forestry Tools

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Find a trunk’s diameter whether it’s sloped, multi-stemmed, or forked
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A tree’s diameter is a useful metric for measuring its size, growth, and volume. You need to know the diameter to calculate the amount of the fertilizer a tree needs and also to determine its value in case you want to sell its wood. Since you probably don’t want to cut down the tree to figure out its diameter, you can measure it with common household items like a ruler or a measuring tape, or with professional specialty tools like a tree caliper or diameter tape. The diameter should always be measured at diameter breast height (DBH) or 4.5 ft (1.4 m) above the average ground level.

How do you measure tree diameter?

For a quick tree diameter measurement, wrap a cloth tape measure or string around the trunk at diameter breast height (DBH), or 4.5 ft (1.4 m) above average ground level. Measure the distance around the tree and divide by pi (3.1416) to get the diameter. For the most accurate reading, use forestry diameter tape.

Method 1
Method 1 of 2:

Making Quick Tree Diameter Measurements with Household Tools

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    This is a great technique for a quick estimate, but not ideal for taking a precise measurement. Hold the ruler against the tree at diameter breast height (DBH), or 4.5 feet (1.4 m) above ground. Line up the left edge of the ruler with the left edge of the tree and read the measurement where the right side of the tree visually lines up with the ruler.
    • This method is best only when you want a very rough and fast estimate of a tree’s diameter.
    • If the tree is growing on a slope, measure DBH on the uphill side of the trunk. [1]
    • If the tree has a split or forked trunk, measure the trunk just below the fork as close to DBH as you can. [2]
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    Just wrap a common measuring tape all the way around the middle of the tree at DBH. Record the circumference at the point where the two ends of the tape meet. [3] Then, all you need to do to calculate the diameter is divide that number by pi (3.1416).
    • Using a cloth measuring tape (like a tailor would use) is better than a common household metal tape measure because it is more flexible and will conform to the shape of the tree.
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    For this method, wrap a long string around the tree at DBH and cut the string where it meets. Then, measure that length with a measuring tape or yardstick to find the circumference. [4] Divide that number by pi (3.1416) to get the diameter. [5]
    • Using a string to take the circumference measurement is more accurate than using a measuring tape because the string is more flexible and bends easier to the tree.
    • If the tree is very big, recruit a friend to help with this method or bring along a thumb tack to secure the string to the tree.
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Method 2
Method 2 of 2:

Measuring Tree Diameter with Specialty Tools

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    To use a tree caliper , open the caliper wider than the tree, place its arms on either side at DBH, and close the caliper as tight as it will go around the tree. Then, read the number on the caliper at the point where the lower arm stopped on the guide to find the diameter. [6]
    • If the tree is not perfectly round, take two measurements: one on the wider side of the trunk, and one on the narrow side. Then, calculate the average of both by adding them together and dividing by 2. [7]
    • If the tree is leaning at an angle, hold the caliper at the same angle of the lean to keep it perpendicular to the tree.
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    Hold the tree-scale stick against the tree at DBH, 25 in (64 cm) from your eyes. Then, line up the left edge of the stick to the left edge of the tree and read the number on the stick that lines up with the right edge of the tree. [8]
    • Like the ruler method, this is not the most accurate way of measuring diameter, but is useful if you want a rough estimate.
    • Tree-scale sticks are also known as Biltmore sticks.
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    Diameter tape or “D-tape” is the most common tool that foresters use to measure tree diameters. All you have to do to use the tape is wrap it around the tree at DBH and read the number where the tape meets. This number is the diameter of the tree and there are no further calculations necessary. [9]
    • Even if your tree is irregularly shaped, the D-tape method provides a close and acceptable estimate. [10]
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    In this formula, d is the total diameter of the multi-stemmed tree, x is the diameter of the largest stem, and y is the diameter of all other stems combined. To start, measure the diameter of each stem. Then, add the full diameter of the largest trunk ( x ) to half of the diameter of each additional trunk ( y ). The result is the total diameter of the multi-stemmed tree ( d ). [11]
    • For example, if you have 4 stems measuring 7, 6, 6, and 4 inches, you’d add 7+((6+6+4)/2), or 7+(16/2), to get a total diameter of 15 inches.
    • If the stems split apart closer than 6 inches (15 cm) from the ground, then they are considered separate trees and should be measured individually.
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      References

      1. ↑ https://extapps.dec.ny.gov/docs/lands_forests_pdf/dbhguidelines.pdf
      2. ↑ https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5202838.pdf
      3. ↑ https://www.mass.gov/how-to/how-to-measure-trees
      4. ↑ https://www.mass.gov/how-to/how-to-measure-trees
      5. ↑ https://youtu.be/XXubnEy381Y?t=244
      6. ↑ https://openoregon.pressbooks.pub/forestmeasurements/chapter/3-3-instruments-for-measuring-tree-diameter/
      7. ↑ https://youtu.be/XXubnEy381Y?t=135
      8. ↑ https://openoregon.pressbooks.pub/forestmeasurements/chapter/3-3-instruments-for-measuring-tree-diameter/
      9. ↑ https://extension.missouri.edu/publications/g5050
      1. ↑ https://openoregon.pressbooks.pub/forestmeasurements/chapter/3-3-instruments-for-measuring-tree-diameter/
      2. ↑ https://www.austintexas.gov/sites/default/files/files/Watershed/field_operations/Tree_Ordinance_Review_Permit_Diagram.pdf

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