Trees are measured with a standard measurement called DBH, or Diameter at Breast Height. DBH is the tree's diameter 4.5 feet above ground level.
Foresters and arborists often use a special measuring tape called a d-tape that displays diameter measurements when wrapped around a tree's circumference. But because OpenTreeMap calculates the diameter for you, you can use any flexible tape measure or even a piece of string to find the DBH by measuring the circumference.
First, measure 4.5 feet up the tree trunk from the ground. If you have a partner, they can place their finger at the appropriate height, otherwise you can use a small tack to mark the spot. If there is a branch or large bump at 4.5 feet, you should measure slightly above or below it to get a more accurate measurement.
Then wrap your measuring tape tightly around the the tree trunk at 4.5 feet and enter this measurement into the OpenTreeMap circumference field.
If you are using a string, wrap the string tightly around the tree trunk at 4.5 feet and mark or cut the circumference on the string. Then measure the length of the string, and enter this measurement into the OpenTreeMap circumference field.
OpenTreeMap will automatically calculate the diameter, or DBH for you.