What this calculator does
The Tree Diameter Calculator converts an easy-to-measure trunk circumference (wrapping a tape measure around the trunk at breast height, about 4.5 feet / 1.3 meters up) into diameter at breast height (DBH), the standard measurement foresters and arborists use to track tree size and growth.
The formula it uses
Since a tree trunk is treated as a circle, diameter is calculated from circumference using Diameter = Circumference / π. The calculator also reports the trunk’s radius and cross-sectional area (Area = π × radius²), and converts the diameter to the other common unit system.
A note on accuracy
Real trunks are rarely perfectly round, and bark thickness, buttressing, or measuring at an angle can all introduce small errors. For consistent results, measure circumference at a standard breast height on a level part of the trunk with the tape held snugly but not compressed.