Enter the total girth of a tree and the growth rate into the calculator to determine the estimated age of the tree.

Tree Age Formula

The following formula is used to estimate the age of a tree.

TA = G / GR

  • Where TA is the tree age (years)
  • G is the girth (diameter) at about 2-3 feet off the ground
  • GR is the growth rate (growth factor) of the tree

Tree Age Definition

What is a tree age? Tree age is the estimated amount of time that a tree has been alive. This can typically be estimated using the girth of a tree and its growth factor, also known as the growth rate.

Example Problem

How to calculate tree age?

  1. First, measure the girth 2-3 feet above the ground.

    For this example, the girth is measure to be 50cm.

  2. Next, determine the growth rate.

    The average growth rate of the girth of a tree per year is around 2.5cm per year until it stops growing.

  3. Finally, calculate the age of the tree.

    Using the formula, we find the tree to be 20 years old.


How is tree age determined? Tree age can be estimated using the formula above. The more accurate way of determining a tree age is through radioactive isotopes that are found in the tree itself.

What is the maximum age of a tree? The maximum age of a tree depends on the type of tree. The oldest trees in the world are the Great Basin Bristlecone Pine, and these can live to 5,000 years old or longer.

Do rings show a trees age? While rings in the trunk of a tree can be used to estimate the age of a tree, they do not provide an exact answer.

tree age calculator
tree age formula