The short answer is, measurements & math.

With the right information, it’s not hard to determine the age of your timber within a year or two of accuracy. Here’s what you do:

STEP 1: Measure the circumference of a given tree in inches about five feet up from the base.

STEP 2: Find the “growth factor” for that species of tree from the list further down on this page. Different species of tree have different growth factors, determined by a wide variety of data.

STEP 3: Multiply your measurement from step one by this growth factor to arrive at a rough estimate as to the age of the average tree of that species with a similar diameter.

Common Timber Growth Factors:
Pine: 0
Red Maple: 5
Silver Maple: 0
Sugar Maple: 0
River Birch: 5
White Birch: 0
Shagbark Hickory: 5
Green Ash: 0
Black Walnut: 5
Black Cherry: 0
White Oak: 0
Red Oak: 0
Pin Oak: 0
Linden or Basswood: 0
American Elm: 0
Ironwood: 0
Cottonwood: 0
Dogwood: 0
Redbud: 0