A well-known tree expert, M. W. Staples of Kent Ohio, has been credited with developing guidelines for estimating the age of large trees.

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The formula is as follows:

Tree diameter in inches multiplied by tree species multiplier = tree's approximate age.

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Measure the circumference of your tree in inches at 4 ½ feet from the ground. Divide the result by 3.14 (π).
Then for the species you have selected, use the approximate multiplier as listed below to determine approximate age.