D = C / π | Measure circumference at 4.5 ft (DBH)
DBH (Diameter at Breast Height) is measured at 4.5 feet (1.37 m) above the ground on the uphill side. It's the most common tree measurement in forestry. Since diameter is hard to measure directly on standing trees, foresters often measure circumference with a tape and divide by π: D = C/π. Diameter tapes (D-tapes) are pre-calibrated to read diameter directly from circumference. Calipers can measure diameter directly on small trees. DBH is used to calculate: basal area, volume, biomass, and carbon storage. In forestry inventories, trees are tallied by 2-inch DBH classes. Minimum merchantable timber size: typically 10-12" DBH.