Tree rules explained
How to Measure Tree Diameter (DBH) for a Permit
Municipal tree bylaws often use diameter at breast height. Here is how to read the local rule without mixing measurement heights or multi-stem formulas.
What DBH means
DBH means diameter at breast height. It is a standardized way to describe trunk size, but municipalities do not always use exactly the same measurement height or multi-stem formula. That is why the local bylaw matters.
Do not measure circumference and call it diameter
If you wrap a tape around the trunk you have measured circumference. To estimate diameter from circumference, divide by π (about 3.1416). A forestry diameter tape does this conversion automatically.
Check the required height first
Many Canadian municipal guides use a measurement around 1.3 to 1.4 metres above grade. Toronto, Vancouver, Cambridge and other cities publish their own measurement definitions. Use the number in the municipality's rule, not a generic internet value.
Multi-stem trees can be different
Some bylaws specify how to combine stems or classify multi-stem trees. New Westminster, for example, has a specific protected-tree definition for certain multi-stem trees. Do not simply measure the largest stem unless the local rule tells you to.
Slopes and unusual trunks
Leaning trunks, buttress roots, forks and grade changes can make a simple measurement ambiguous. If the tree is near the threshold, ask the municipality or a qualified arborist how that bylaw expects the tree to be measured.
Why accuracy matters
A centimetre or two can determine whether a size-based permit rule applies. Photograph the measurement and keep the municipal definition with your project notes before you hire a contractor.
Official sources used
Sources checked September 13, 2026. Rules can change and the exact property/tree can change the answer. Confirm the current municipal requirement before work begins.