DBH (Diameter at Breast Height)
ArboricultureA standard measurement of tree trunk diameter taken at 4.5 feet (1.37 meters) above ground level, used for inventory, assessment, and regulatory purposes.
Diameter at Breast Height (DBH) is the standard measurement used to describe tree size. It is taken at 4.5 feet (1.37 meters) above the ground on the uphill side of the tree. This standardized measurement point allows consistent comparison between trees and over time, and it forms the basis for many tree ordinances, preservation standards, and management calculations.
DBH is measured using a diameter tape (D-tape) that wraps around the trunk and reads directly in diameter, or with calipers for smaller trees. When the trunk is irregular, forked below breast height, or growing on a slope, specific conventions dictate where and how to measure. For multi-stemmed trees, each stem is typically measured separately.
This measurement is used extensively in urban forestry for tree inventories, determining tree protection requirements, calculating replacement values, and assessing canopy cover. Many municipal tree ordinances use DBH thresholds to define heritage or significant trees that receive extra protection. For example, a city might require a permit to remove any tree over 12 inches DBH. The measurement also drives formulas for estimating tree preservation zones during construction.