Do you measure diameter at your breast height?

 What is DBH?

"DBH is shorthand for the diameter of a tree’s trunk measured at breast height... probably the most common and important measurement made on standing trees"

"In the U.S., DBH is the diameter of a tree stem measured at 4.5 feet above the ground. In Canada, Europe, and most of the rest of the world, “metric DBH” is measured at 1.30 meters (4 feet, 3.2 inches). In Japan and Korea, it’s 1.20 meters, and in New Zealand, it’s 1.40 meters"

"DBH is also supposed to be measured on the uphill side of the tree (from the duff, not the soil), perpendicular to the lean of the tree, and above any branches, burls, swellings, or other protuberances that may exist at that height."

https://openoregon.pressbooks.pub/forestmeasurements/chapter/3-2-determining-tree-diameter/

Why 4.5 feet? 

"To make tree diameter measurements meaningful and easy to perform, a standard location and protocol have been developed. Diameters are measured outside the bark at 4.5 feet above the ground on the uphill side of the tree (Figure 3.3). This location, called diameter at breast height or DBH, is above most butt swell and brush. It is also at a comfortable arm position for most people."

Here is an article focusing on the origin of 4.5 feet.

"In 1899, Gifford Pinchot—arguably the most important forester in U.S. history—claimed that 4.5 feet (ft) (137 cm) was the customary height for measuring the diameter of a tree’s trunk, which then became the default height in the United States. However, based on my review of archival forestry texts, there was wide variation in the heights used to measure trees pre-1900. Furthermore, my analysis of male anthropometric datasets contradicts assertions that 4.5 ft is a comfortable measurement height for men. Rather, 4.5 ft was likely Pinchot’s own BH. The selection of 4.5 ft might have also resulted from a mis-conversion of Bavarian forestry data. I discuss the social context in which the 4.5 ft standard emerged."