Tree Diameter Calculator
Convert trunk circumference to diameter at breast height (DBH). The standard tree measurement.
Measure around the trunk at 4.5 feet above ground
What is DBH and why is it measured?
DBH (Diameter at Breast Height) is standard forestry measurement: trunk diameter 4.5 feet (1.37m) above ground. It is used to: estimate tree volume and timber value, assess tree age, compare trees, plan management, and calculate carbon sequestration. 4.5 feet represents breast height for standing humans - an easy, consistent reference point. DBH is the key input for forest inventory, timber cruising, and urban tree assessment.
How do I measure trunk circumference accurately?
Use a flexible tape measure at breast height (4.5 ft). Wrap snugly but not tight. For sloping ground, measure on the uphill side. For leaning trees, measure perpendicular to lean. For multi-stem trees, measure the largest stem, or add areas for each stem. Mark your spot so you can re-measure in the same place. Take multiple measurements at different heights for irregular trunks and average them.
How do I convert between circumference and diameter?
Diameter = Circumference ÷ π (3.14159). Example: 37.7" circumference ÷ 3.14 = 12" diameter. For DBH in centimeters: circumference in cm ÷ π = diameter in cm. Many forestry tapes show diameter directly on one edge - "Diameter in inches" or "DBH" marked. Using a diameter tape is the most accurate method as it converts automatically. Remember: growth is not perfectly circular for some trees.
What if my tree is forked below 4.5 feet?
For forked trunks: measure below the fork if possible, or calculate individual stem areas: DBH = √(stem1² + stem2² + ...). This gives "equivalent DBH" of a single stem. Alternatively, measure each stem at 4.5 ft separately. For severely irregular trunks, measure at multiple heights and use an average. Document the measurement location and method in your records for consistency.