The most reliable way to determine the age of a tree is to count the number of growth rings in the trunk, either in a felled tree or from a core slice taken with a borer. But you can also determine the approximate age of a tree by measuring its diameter at breast height (4 feet 6 inches high) and using a formula to convert that into years.

However, there are lots of variables involved. These include site conditions, sun exposure and geographic location. There can be a big difference between a tree growing in a forest and a tree growing in the open. The species of the tree is also important, as some trees grow faster than others and have different-width growth rings.

Determining the age of a standing tree you can use a formula; more here.

For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service