Most of the emails we get asking whether a tree needs a permit could have been answered with a tape measure. The question is almost never about the tree’s health or species. It’s about one number: the diameter at breast height, or DBH. Get that number, compare it to your city’s threshold, and half the uncertainty is gone before you’ve spoken to anyone.
The Number That Decides Everything
Most GTA tree bylaws set their permit threshold as a trunk diameter. Toronto’s Chapter 813 of the Municipal Code sets the cutoff at 30 cm. Markham’s By-law 2023-164 sets it at 20 cm. Oakville’s Private Tree Protection By-law sets it at 15 cm. A tree at or above the local threshold needs a permit before it can be removed or injured. A tree below it may still be regulated because it is city-owned, on a boundary, inside a ravine or woodland, protected by a development condition, or affected by another municipal rule.
Not every municipality works this way. A few, including some in Durham Region, use zone-based permit rules instead of a diameter threshold, or have no per-tree bylaw at all outside woodlots.
Diameter isn’t measured at the base, where trunks flare out and inflate the reading. It’s measured higher up the trunk, at a height each municipality sets in its bylaw. Toronto measures at 1.4 metres. Markham measures at 1.37 metres. Vaughan’s Tree Protection By-law 177-2025 is the outlier: it sets its 20 cm threshold by base diameter instead of breast height, so a Vaughan property needs a different measurement point altogether. Check your own city’s height and threshold on our permit checker or the full bylaw comparison by city before you pick up a tape.
The Method, Briefly
Wrap a flexible tape around the trunk at the right height, level and snug against the bark, and divide the circumference by 3.1416 to get the diameter. A trunk that splits into two or more stems below breast height needs a different formula, not a simple sum of the stems, and a lean or fork near breast height throws the reading off if you measure straight up from the ground instead of along the trunk. The full method, worked example, and diagram are on our how-to-measure-DBH page.
When the Reading Is Close Enough On Its Own
If your tree measures well clear of your municipality’s threshold, a tape measure may settle the diameter question. It does not settle ownership, ravine, woodland, development, or site-specific protections. Check those layers before concluding that a permit or arborist report is unnecessary.
When a Tape Measure Stops Being Enough
The reading stops being sufficient in a few specific situations. If the number lands within a few centimetres of your city’s cutoff, rounding and tape placement start to matter more than they should. If the trunk has a fork, buttress roots, or a pronounced lean right at breast height, the wrap point itself is ambiguous, and two people measuring the same tree can land on different numbers. And if a neighbour or the city disputes your reading, your own tape measurement carries no documentation behind it.
A city’s forestry department reviewing a permit application isn’t looking for a homeowner’s tape reading. It wants a measurement it can rely on: the point on the trunk, the method used, and who took it. A tree removal report from an ISA Certified Arborist provides exactly that, tied to a specific height and method that stands up if the number is ever questioned.
Measure First, Call If You Need To
Measure first. The tape and a calculator will often tell you the call isn’t necessary at all.