This page gives two ways to estimate the age of your tree:  a lookup table and an age ‘calculator’.   Keep these things in mind:

• These two methods give different results for the same tree.  The Estimated Age Lookup Table gives smaller, more conservative ages and we believe may be more correct because the data is non-linear and varies by species.
• Most foresters and tree experts say that there is a margin of error for estimating age based on whether the tree is in a natural or urban forest.  The interesting thing is that these sources are divided on whether an urban tree will 1) grow faster because it’s being pampered by being watered and looked after, or 2) will grow slower because it’s under duress from its life in a toxic city environment.
• Locating the origin of the growth factor data has been difficult.  We compiled our chart from multiple sources and fortunately they all gave the same number for any given species.  They probably all relied on one study, but we not able to locate that study.  The International Society of Arboriculture was cited by several.

We’ve cited sources for each method, so you you can investigate further.   The bottom line is the estimated age is just that – an estimate.

Estimated Age Lookup Table

This is a table that we reproduced from the Morton Arboretum, Determining the Age and Benefits of a Tree.  It has fewer species than the Tree Growth Factors by Species table below, but if your species is listed, it’s a bit quicker to use and we think the information might be more dependable.

For starters, this shows that growth rates are not linear and the curves vary by species.  A Green Ash tree with a diameter of 10 inches is 27 years old while a 30-inch tree is 104 years old: 3 times the size yields almost 4 times the age.   By comparison, a Silver Maple with a diameter of 10 inches is 9 years old and at 30 inches is 65 years old: 3 times the size gives 7 times the age.

[1]  The Morton Arboretum: Determining the Age and Benefits of a Tree

Estimated Age Calculator

The table below has more species than the age calculator but will produce a linear result: 3 times the diameter will give 3 times the age.  Compare this with the table results above.

[2]  About.com: Estimating a Tree’s Age    and   article source: Steve Nix
[3]  Learner.org:  How Old is Your Tree
[4]  State of Maine DNR: Growth Factor Worksheet
[5]  International Society of Arboriculture