Instead, defects and structural anomalies cause bumps and swellings that make measurements difficult. To allow measurements of bole size to be compared, a standard point on the trunk is defined. This standard height is termed breast height. The actual location of breast height varies slightly between some countries. In continental Europe, Australia, U.K, Canada and some former members of the British Commonwealth breast height is defined as 1.3 m above the ground.
Breast height is a convention with a long history of use within forestry practice.
However, other standard heights are also used. Some researchers in grazing and agriculture use bole size at 0.3 m or 0.7 m above the ground as their standard height. For example, the volume of the tree bole may not be correlated with a measurement at a height that corresponds to a fork in the tree or a fire scar. If the fork is above breast height, treat the tree as a single stem with multiple leaders. When swelling at breast height occurs due to multiple leaders, the breast height measurement is conventionally taken where the bole diameter is smallest below the swelling.