Article in English: Average breast height, which is a forestry measurement, is 4 1⁄2 ft (1.4 m) from ground level. Wrap a fabric measuring tape around the trunk at this height, and note the tree’s circumference.  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. To find the diameter, divide the circumference by pi, or approximately 3.14. Then find the radius by dividing the diameter by 2. 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). For tree species with thick bark, such as black oak, subtract 1 in (2.5 cm) from the radius measurement. Subtract 1⁄4 in (0.64 cm) for species with thin bark, such as birch. If you’re not sure and just want a rough estimate, subtract 1⁄2 in (1.3 cm) from the radius. Including the bark would add extra girth and throw off your measurements. Check around the tree in question for dead or fallen trees of the same species. If you find one with visible rings, measure the radius and count the rings. Then divide the radius by the number of rings to find the average ring width.  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. If you can’t find any nearby stumps or felled trees, search...

Summary in Vietnamese:
Đo chu vi thân cây ở độ cao ngang ngực. Tìm đường kính và bán kính thân cây. Trừ đi 0,6 cm đến 2,5 cm phần vỏ cây. Sử dụng các cây tương tự đã ngã đổ để tính độ rộng trung bình vòng tròn trên mặt cắt ngang thân cây. Tra cứu tốc độ tăng trưởng trung bình của loài cây, nếu cần thiết. Chia bán kính cho độ rộng trung bình vòng. Chia chu vi thân cây cho tốc độ tăng trưởng năm.