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This article was reviewed by Ben Barkan and by wikiHow staff writer, Dan Hickey. Ben Barkan is a Garden and Landscape Designer and the Owner and Founder of HomeHarvest LLC, an edible landscapes and construction business based in Boston, Massachusetts. Ben has over 12 years of experience working with organic gardening and specializes in designing and building beautiful landscapes with custom construction and creative plant integration. He is a Certified Permaculture Designer, Licensed Construction Supervisor in Massachusetts, and a Licensed Home Improvement Contractor. He holds an associates degree in Sustainable Agriculture from the University of Massachusetts, Amherst.
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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.
Steps
Making Quick Tree Diameter Measurements with Household Tools
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![Step 1 Use a common 12 inch (30 cm) ruler to roughly measure a small tree.]()
Use a common 12 inch (30 cm) ruler to roughly measure a small tree. 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. -
![Step 2 Find the tree's circumference with a measuring tape and divide by pi.]()
Find the tree's circumference with a measuring tape and divide by pi. 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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![Step 3 Measure circumference precisely with a string, then calculate diameter.]()
Measure circumference precisely with a string, then calculate diameter. 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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![Step 1 Take an easy measurement with a tree caliper.]()
Take an easy measurement with a tree caliper. 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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![Step 2 Hold a tree-scale stick up to the tree for an estimated measurement.]()
Hold a tree-scale stick up to the tree for an estimated measurement. 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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![Step 3 Get the most accurate measurement by wrapping D-tape around the trunk.]()
Get the most accurate measurement by wrapping D-tape around the trunk. 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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![Step 4 Measure multi-stemmed trees with the formula d=x+(y/2).]()
Measure multi-stemmed trees with the formula d=x+(y/2). 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.
Expert Q&A
Tips
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You can find the professional tools at some larger hardware stores or buy them online.Thanks
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If your tree is on a slope, measure DBH from the uphill side of the slope.Thanks
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Call a forester for assistance if the tree is too big or too dangerous to access.Thanks
References
- ↑ https://extapps.dec.ny.gov/docs/lands_forests_pdf/dbhguidelines.pdf
- ↑ https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5202838.pdf
- ↑ https://www.mass.gov/how-to/how-to-measure-trees
- ↑ https://www.mass.gov/how-to/how-to-measure-trees
- ↑ https://youtu.be/XXubnEy381Y?t=244
- ↑ https://openoregon.pressbooks.pub/forestmeasurements/chapter/3-3-instruments-for-measuring-tree-diameter/
- ↑ https://youtu.be/XXubnEy381Y?t=135
- ↑ https://openoregon.pressbooks.pub/forestmeasurements/chapter/3-3-instruments-for-measuring-tree-diameter/
- ↑ https://extension.missouri.edu/publications/g5050
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