Tree Age Calculator: How to Estimate a Tree’s Age

To calculate a tree’s age, enter the diameter and then select the tree species. If you can’t find your specific tree, simply choose the “enter the growth factor” option and insert the number manually.

Keep in mind that many environmental conditions affect growth rate, so estimating the age of a tree with this method is only approximate.

There is also a variation in growth rate between urban-grown and forest-grown trees.

Tree Diameter Calculator

Tree Age Calculator

Tree Age Formula

To determine the approximate tree’s age, we need to calculate:

Tree Age = diameter (in inches) x growth factor

Tree diameter = circumference ÷ 3.14 (pi)

Let’s say we want to calculate an approximate red oak’s age with a circumference of 31.4 inches. When we divide that by 3.14 (31.4 ÷ 3.14), we’ll determine that the tree diameter is 10 inches. Red Oak’s growth rate factor is 4. That means the tree would be roughly 40 years old. (10×4=40).

Oak Tree Age Calculator

How to Estimate Tree Age Step by Step

Identify the Tree Species

Determine the type of tree you are measuring. If you need help identifying the tree, use iNaturalist or Pl@antNet mobile application. These apps use image recognition technology to help identify plants and trees.

Calculate the Tree’s Diameter

Person calculating tree age by measuring the diameter of a tree trunk with a diameter tape measure against a rough bark surface, in a setting with a wrought iron fence and red brick building in the background.

To determine the circumference, start at about 4 1/2 feet above the ground, which is roughly at chest height.

Measure the circumference using string, fabric measuring tape or diameter tape. Encircle the trunk with the string, and either mark or trim the point where it overlaps. Afterward, measure the length of the string for your result.

Diameter = Circumference ÷ 3.14

Find the Tree’s Growth Factor

Check tree species and their tree growth rate in the chart below.

Calculate the Tree’s Age

Multiply the diameter in inches by your tree’s growth factor to get a more accurate estimate of the tree’s age, or use our tree age calculator. For instance, a Horse Chestnut tree with a trunk diameter of 6 inches and a growth factor of 8 would have an estimated age of 48 years (Diameter in inches x Growth Factor = Tree Age).

Estimating Tree Age by Growth Rings

Another method of estimating a tree’s age is to examine its growth rings, which can be seen in a cross-section of a tree trunk.

Each ring typically represents one year of growth, making it possible to determine a tree’s age by counting its rings.

However, this method requires access to a cross-section of the tree, which is possible only after the tree is cut down.

Can you tell how old the tree in the picture below is by calculating the number of growth rings?

Close-up of a tree's cross-section on a white background, displaying concentric growth rings and natural bark edging

Factors Influencing Tree Growth Rates

In optimal conditions and with proper tree care, trees grow approximately 1 inch of new trunk circumference every year. So to get a rough estimation, a tree with a 12-inch circumference is approximately 12 years old.

However, many factors influence tree growth rate. Not to mention that every tree species grows at a different pace, so the “Tree Age Formula” or calculating growth rings is a lot more accurate.

Environmental conditions that affect the tree’s growth rate include:

  • Water Availability: Adequate water is crucial for tree growth. Drought conditions can significantly slow growth.
  • Climate: Temperature and sunlight affect photosynthesis and growth rates.
  • Soil Conditions: Nutrient-rich, well-drained soil supports healthier growth than poor soil.
  • Root Stress: Compacted soil, damage, or disease can restrict a tree’s ability to absorb water and nutrients, slowing growth.
  • Competition for Light: Trees in dense forests or shaded areas may grow slower as they compete for sunlight.
  • Overall Plant Vigor: A tree’s general health and vigor, influenced by all the above factors, determine its growth potential.

Side Note: One way to get an average growth rate is by measuring the tree’s change in size and dividing it by the amount of time it has been growing.

Tree Growth Factor Chart

TreeGrowth Rate
American Beech6
American Elm4
Aspen spp2
Basswood3
Black Cherry5
Black Walnut4.5
Bradford Pear3
Colorado Blue Spruce4.5
Cottonwood2
Douglas Fir5
European Beech4
European White Birch5
Green Ash4
Horse Chestnut8
Ironwood7
Kentucky Coffee Tree3
Littleleaf Linden3.5
Norway Maple4.5
Norway Spruce5
Pin Oak3
Red Maple4
Red Oak4
Redbud7
River Birch3.5
Scarlet Oak4
Shingle Oak6
Shagbark Hickory7.5
Silver Maple3
Scotch Pine3.5
Sugar Maple5.5
Sweet Gum4
Tulip Poplar3
White Ash5
White Birch5
White Fir7.5
White Oak5
White Pine5
Yellow Buckeye4

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