How Old is That Tree?
You don't need to cut down a tree and count its growth rings or use an increment borer to find out how old it is. You can make a fairly good estimate of a tree’s age using a simple formula published by the International Society of Arboriculture.
- First, determine tree diameter in inches measured at 54 inches above ground level.
- Remember that diameter equals circumference divided by 3.14 (pi).
- Use the following table, which assigns a growth factor to various tree species. Multiply the diameter in inches by the appropriate growth factor to determine the estimated age of your tree. Let's use the white oak, for example. It has a growth factor of 5. If our white oak has a diameter of 22 inches, we'd multiply that by 5 to get an estimated age of 110 years.
Note: The growth factors listed below are more accurate for forest-grown trees, which grow thinner than street trees. Stressed trees from urban situations—such as inadequate soil, damage or topping—will grow slower and weaker than healthy trees.
Tree species and related growth factors
Diameter in inches x growth factor = tree age
|Bradford pear (invasive non-native, not recommended)||3|
|Colorado blue spruce||4.5|
|European white birch||5|
|Kentucky coffee tree||3|
|Northern red oak||4|