Tree Age Calculator
Enter the trunk diameter (DBH) or circumference at breast height and the growth factor for your species, then read a rough age estimate. Growth factors vary widely by species and site, so you supply the number rather than relying on a built-in table.
Last updated: September 25, 2026
Frequently asked questions
Where do I find the growth factor for my tree?
Look for a growth factor for your species in a forestry extension service, arborist association, or university publication. The factor is expressed as years of age per inch of trunk diameter, and this calculator deliberately does not include a table of values because they vary by region and site.
How accurate is a tree age estimate from diameter?
It is a rough guide. Two trees of the same species and diameter can differ in age by decades because of soil, moisture, crowding, and pruning. Treat the result as an order-of-magnitude estimate, not a certified age.
How do I measure DBH or circumference?
Measure at breast height, 4.5 feet (1.37 m) above ground on the uphill side. Wrap a tape around the trunk for circumference, or use a diameter tape or calipers for DBH. The Basal Area Calculator explains DBH in more detail.
Can I get an exact age without cutting the tree?
An increment borer removes a thin core you can read ring by ring without felling the tree, and some trees have records such as planting dates. Ring counts on a stump or core are far more reliable than any diameter-based formula.
Why is the result different from what I expected for an old or fast-growing tree?
A single factor assumes steady growth. Open-grown trees tend to grow faster than forest trees, and very old trees slow down, so the factor should match the conditions your tree grew in.
Does this work for shrubs or multi-stem trees?
It is meant for single-stem trees. For multi-stem trees, measure the largest stem and treat the estimate with extra caution.