5041 Guide Meridian Rd. Bellingham, WA 98226

Call for a Free Estimate


A tree’s age provides a wealth of information. However, have you ever wondered how to determine the age of a tree? In this post, Timber Tree Service highlights various ways to determine a tree’s age.

As Bellingham’s tree service company, count on us for all your tree-related needs.

Counting the Rings of a Stump

Counting rings on a stump helps to determine a tree’s age accurately. This method works if you have a fallen tree nearby of the same or approximate age. Nobody wants to kill a tree just to determine its age.

When counting the rings of a stump, look inside the core for annual circles or growth rings. Count the rings of each annual circle, beginning with the innermost part of the core and moving outward toward the bark.

Measuring the Tree Trunk’s Circumference

For this method, use a fabric tape measure or string to measure the tree’s breath at about 4.5 feet from the ground. Once you have the circumference, divide it by pi (3.14) to get the diameter, then divide the diameter by two to get the radius.

For example:

A circumference of 170 ÷ 3.14 = 54 inches (diameter)

54 inches (diameter) ÷ 2 = 17 inches (radius)

Next, subtract the thickness of the bark from the radius. Most species of trees have a bark ranging between 0.25 and one inch. Assuming a bark of 0.8 inches, calculate the radius without the bark as:

17 inches (radius) – 0.8 inches = 16.2 inches (radius without bark)

Perhaps you had a tree on your property that has been cut down with the stump intact. Counting the number of rings and measuring the radius gives you the average ring width.

For example, a tree stump with a 20-inch radius and 80 rings will have an average ring width of:

20-inch radius ÷ 80 rings = 0.25 inches (average ring width)

Assuming an average ring width for the tree you plan to measure, estimate the tree’s age by dividing the radius by the average ring width.

16.2 inches (radius without bark) ÷ 0.25 inches (average ring width) = 65 years.

If you don’t have a stump on your property, estimate the tree’s age by dividing its circumference by the average growth rate of the tree in question. Look online for growth factors based on tree species.

If the tree has an annual growth rate of two inches, you can calculate the age estimate as follows:

170 inches (circumference) ÷ 2 inches (annual growth rate) = 85 years

Counting Branch Whorls

Tree age information also helps with conservation. Another tip on how to determine the age of a tree includes counting the whorls that wrap around the trunk. Whorls refer to the circular growth of branches at approximately the same height around the tree trunk.

This technique works for conifers or evergreens but isn’t very useful for broadleaf trees. Simply count from the bottom whorl up to tell the tree’s age.

Counting Rings on a Core Sample

Using an increment borer to take a core sample of a living tree allows you to estimate its age. An increment borer refers to a T-shaped instrument that you can use to drill into a tree and take a thin sample of the tree’s core.

Once you bore out a sample, cover the hole to keep the tree alive, then count the rings on the sample to determine the tree’s age.

Contact Your Local Tree Care Experts

If you need comprehensive tree services, trust your local arborists at Timber Tree Service. Contact us at (360) 441-5033 for more information on how to determine the age of a tree or signs your tree is dying.

Call Now Button