How Old Is That Tree? Pettengill Woods Trail Field Day

Did you know that trees are the largest plants on earth? Some trees can grow to be thousands of years old and hundreds of feet high. You don't have to chop down a tree and count the rings to estimate its age. All you need is a calculator and measuring tape!

1. From the base of the tree measure 4 1/2 feet up the trunk. At the 4 1/2 foot mark, measure the distance around the trunk (the circumference). Write down the circumference in inches.

Circumference =

2. Use this formula to determine the diameter, (distance through the trunk) also called the Diameter at Breast Height, or DBH. Then write the DBH down in inches.

Circumference divided by 3.14 = DBH
DBH =

3. Get the growth rate of your tree from the list below. Then multiply your tree's diameter by its growth rate. The result is the approximate age of your tree!

Diameter x growth rate = age
Approximate Age =


Here's your formula!

Circumference=
Circumference divided by 3.14 = DBH (diameter)
DBH (diameter) =
DBH (diameter) x growth rate (below) = age
Approximate Age =


Tree Growth Rate Chart

Most trees grow an average of one inch in diameter each year. Some trees, like the ones below, grow more slowly. For example, mature American Elms take about four years to grow one inch in diameter. To estimate the age of a tree, find the tree in the list below and use the number shown in step 3. If you don't see your tree below, use a growth rate factor of one.

American Elm 4
Ash 4
Aspen 2
Basswood 3
Black Cherry 5
Black Walnut 4.5
Cottonwood 2
Dogwood 7
Ironwood 7
Pin Oak 3
Red Oak 4
Redbud 7
Red Maple 4.5
River Birch 3.5
Shagbark Hickory 7.5
Silver Maple 3
Sugar Maple 5
White Birch 5
White Oak 5