Time for another edition of Oaklee Does Math for Pie! Actually, it’s pi day so we’ve enlisted everyone’s favorite squirrel to teach you a bit more about how to use pi to estimate the age of a tree.

For this exercise, you’ll need a tree (forest grown trees work best – trees out in the open grow at different rates depending on site conditions), measuring tape, and a calculator.

Step 1: Identify your tree and find it on the list (below).

Step 2: Measure up to 54 inches from the ground (4 1/2 feet). This is Diameter Breast Height, or DBH.

Step 3: Measure around the tree at DBH to find the circumference in inches.

Step 4: Divide the circumference by the mathematical pi π (3.14). This will give you the tree’s diameter (we learned that last year, remember?).

Step 5: Multiply the diameter by the growth rate number listed next to your tree species in the chart. This will give you the approximate age of your tree! For example, a white oak with a circumference of 126 inches would have a diameter of about 40 inches. Multiply that by the white oak’s growth factor of 5, and you’ll find your white oak is approximately 200 years old.

C/π=d, where C is circumference and d is diameter
d*gr=age, where d is diameter and gr is growth rate number

Growth Rate