How to Measure the Diameter of Trees


The diameter of a round object is tricky to measure directly so the usual way is to start with the circumference and then calculate the diameter. The circumference of a tree is measured 4 1/2 feet above ground level unless it forks at that point, in which case it is measured at the narrowest point below the 4 1/2 ft mark. Once the circumference is known, calculating the diameter is straightforward.

Things You'll Need

  • Tape measure
  • Calculator
  • Measure the circumference of the tree trunk by holding the tape measure 4 1/2 feet above the ground -- at about chest height -- and wrapping it around the tree. Keep the tape tight against the trunk and try to keep it parallel to the ground. Record the value.

  • Convert the measurement into inches. There are 12 inches in 1 foot, so multiply the number of feet by 12 and then add any remaining inches.

    For example, a tree circumference of 8 feet and 8 inches is 103 inches -- (8 x 12) + 8 = 104.

  • Divide the circumference by pi, a mathematical constant usually given as 3.1415. The result is the diameter of the tree.

    For example, given a circumference of 52 inches, the diameter is 16.55 inches because 52 / 3.1415 = 16.55.

Tips & Warnings

  • Keep the tape measure tight around the tree to get an accurate result. A loose tape, or a tape entangled in small branches, adds additional inches to the result.
  • Check the tree of dangers before standing under it. Dead branches, wasp and hornet nests and entangled overhead power lines can lead to injury or death.

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  • Photo Credit Comstock/Comstock/Getty Images
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