About the Tree Age Calculator
This tree age calculator estimates the age of a living tree without cutting or coring it. Measure the trunk circumference at 4.5 feet (about 1.4 m) above the ground, choose the species, and the tool converts the circumference to diameter and multiplies by a species growth factor to give an approximate age in years.
The growth-factor method is widely used by arborists, foresters and curious homeowners to estimate the age of yard trees, park trees and heritage trees. Slow-growing species such as hickory and dogwood have high growth factors (many years per inch of diameter), while fast growers such as cottonwood and aspen have low ones.
The result is an estimate for a forest-grown tree in average conditions. Open-grown trees with plenty of light and water grow faster and may be younger than shown; trees on poor sites or in heavy competition may be older. Counting rings on a core or stump remains the only precise method.
With the default inputs, the estimated age is 95 years. Change any value above to recalculate instantly.
How to use the tree age calculator
- 1Wrap a tape measure around the trunk 4.5 ft (54 in) above the ground.
- 2Enter the circumference and select inches or centimeters.
- 3Choose the tree species, or enter a custom growth factor.
- 4Read the estimated age and compare species in the table.
Formula and method
Diameter at breast height (DBH) is the trunk circumference measured 4.5 ft above the ground divided by π. The growth factor is the average number of years a species takes to add one inch of diameter, so multiplying DBH in inches by the growth factor gives an approximate age. Circumferences entered in centimeters are converted to inches first (÷ 2.54).
Growth factors are averages for forest-grown trees in the northern and central United States. Site, climate, competition and health all change actual growth rates, so treat the result as an estimate rather than an exact age.
- Circumference
- Trunk girth at 4.5 ft (1.37 m) above ground, in inches
- π
- 3.14159…, converts circumference to diameter
- Growth factor
- Years per inch of diameter for the species
Worked examples
White oak with a 60 inch circumference
A 60 inch circumference is a diameter of 60 ÷ π ≈ 19.1 inches. With a white oak growth factor of 5, the tree is roughly 19.1 × 5 ≈ 95 years old.
Silver maple with a 94.25 inch circumference
A 94.25 inch girth gives a 30 inch diameter. Silver maple is a fast grower with a factor of 3, so the estimate is 30 × 3 = 90 years.
Red oak measured at 150 cm
150 cm is 59.06 inches of circumference, or about 18.8 inches of diameter. With a red oak factor of 4 the tree is about 75 years old.
Frequently asked questions
How can I tell how old a tree is without cutting it down?+
Measure the trunk circumference at 4.5 ft above the ground, divide by π to get the diameter, and multiply by the species growth factor. An arborist can also take a thin core sample with an increment borer and count the rings.
What is a tree growth factor?+
It is the average number of years a species needs to add one inch of trunk diameter. For example, silver maple is about 3, white oak about 5 and shagbark hickory about 7.5, reflecting fast, moderate and slow growth.
Why measure at 4.5 feet?+
Diameter at breast height (DBH), 4.5 ft or 1.37 m above ground, is the forestry standard. It avoids the flared root collar at the base and makes measurements comparable between trees.
How accurate is the growth factor method?+
It is a rough estimate intended for forest-grown trees in average conditions, and individual trees can differ from it considerably. Trees in open yards with good soil and water can grow much faster, so the method may overestimate their age.
What if my tree has several trunks?+
Measure each stem at 4.5 ft, square each diameter, add the squares and take the square root to get an equivalent single-stem diameter. Then multiply that by the growth factor.