If the ground is sloped, measure 4 1⁄2 ft (1. 4 m) from ground level on the uphill side, mark the spot, then do the same on the downhill side. The average breast height is the midpoint between the uphill and downhill measurements. For a trunk that forks at a height less than 4 1⁄2 ft (1. 4 m), measure the circumference just below the fork.

For example, if the circumference is 154 in (390 cm), the diameter is approximately 49 in (120 cm), and the radius is about 24 1⁄2 in (62 cm).

Including the bark would add extra girth and throw off your measurements.

Suppose there’s a nearby stump with a radius of 25 in (64 cm), and you count 125 rings. The average ring width would be 1⁄5 in (0. 51 cm). Growth rates vary by tree species and environmental conditions. The living tree you’re measuring probably grew at a rate similar to a tree of the same species that grew nearby. You’ll plug your ring width measurement or, if there are no nearby stumps, an average growth rate into an equation to estimate the tree’s age. Even if you have the average ring width, you can also use the average growth rate to estimate the age, then compare the results of the 2 methods.

In general, a tree is probably around 8-15 years old for every 1 ft (0. 30 m) of trunk diameter. For instance, if the circumference of a tree is 6 ft (1. 8 m) around, it’s probably at least 50 years old if it’s a hardwood. [6] X Expert Source Matt BowmanGardener & Owner, Tradition Market & Garden Expert Interview. 21 April 2020. For example, oak, ash, beech, and sycamore trees grow about 1⁄2 to 3⁄4 in (1. 3 to 1. 9 cm) in circumference per year. If you don’t know the species, plug both 1⁄2 in (1. 3 cm) and 3⁄4 in (1. 9 cm) into your equation to guess an age rage. For a more accurate estimate, factor in the tree’s location. In open conditions, growth rates are usually greater, or 3⁄4 to 1 in (1. 9 to 2. 5 cm) per year. Growth tends to be slower in urban locations and crowded forests. Be sure to check how the growth rate is calculated. Many sources base growth rates on how much the tree’s girth, or circumference, grows per year. However, you might find rates based on the average ring width of the radius.

Say that, excluding the bark, your tree has a radius of about 24 in (60. 96 cm). Using a nearby tree stump of the same species, you calculated an average ring width of 0. 20 in (0. 508 cm). Divide 24 (or 60. 96) by 0. 20 (or 0. 508) to come up with an estimated age of 120 years.

Suppose your tree’s circumference is 154 in (391. 16 cm), and its growth rate is between 0. 75 and 1 in (1. 905 and 2. 54 cm) per year. Divide 154 (or 391. 16) by 0. 75 (or 1. 905), then divide 154 (or 391. 16) by 1 (or 2. 54). Your estimated age range would be between 154 and 205 years old.

Conifers produce whorls annually at regular intervals. Deciduous, or broadleaf trees, produce them irregularly, making it difficult to get an accurate count. It’s also easiest to count the whorls of a young conifer. You might not be able to see the top of a tall, mature conifer, and there would be more irregularities in its growth patterns.

You might see single branches growing between whorls or 2 whorls spaced closely together. These are irregularities that might indicate an injury or unusual weather conditions that year, so don’t count them.

For instance, suppose your tree has 8 recognizable whorls. Beneath the first row, you can see a few stubs that emerge from the trunk around the same level. There’s also a row of 2 or 3 knots under the stubs. You’d count the stubs and knots as additional whorls, so your total count would be 10.

If your whorl count was 10, your final age estimate would be between 12 and 14 years.

The rings can also tell you about the environmental conditions for a particular year. Thinner rings represent colder or dryer years, and thicker rings represent better growing conditions.

You might find that some rings are too close together to see clearly. If necessary, use a magnifying glass to get a better view.

If you have trouble keeping track, try writing a number or making a mark every 10 rings with a pencil.

The length of your increment borer should be at least 75% of the tree’s diameter. You can find increment borers online and at forestry supply stores.

Taking a sample at breast height gives you an estimate called the DBH age. You’ll need to add 5 to 10 years to the DBH age to estimate the tree’s total age. You’ll take the sample at breast height because it’s not practical to take one at the tree’s base. Roots, brush, and the ground would prevent you from turning the handle, and it’s hard to drill while crouching or lying on the ground.

Calculate the tree’s radius to estimate how far you’ll need to drill. Measure the tree’s circumference, divide by pi (about 3. 14) to find the diameter, then divide the diameter by 2 to find the radius.

If you don’t see the pith, place the sample on a large sheet of paper, and extend the curved lines to make full rings on the paper. Based on the rings you’ve drawn, try to guess where the center point would be, and estimate how many rings you’re missing. [18] X Research source

If you have trouble making out the curved lines, sand the sample to make them more visible. Start with 60-grit sandpaper, then finish with a fine grit, such as 400. Remember that your ring count gives you the tree’s DBH age estimate. Add 5 to 10 years to estimate the tree’s total age. [19] X Research source