DBH
Diameter at Breast Height

1.3m and 4.5 ft aren't quite the same number (1.3m is closer to 4.27 ft), but both conventions are in wide use and nobody argues about the 8cm difference in practice. Measure from the ground on the uphill side of the tree if it's on a slope — that keeps the reading consistent with how the next surveyor measures the same tree.

If the stem forks below breast height, you're looking at a multi-stem tree (see below), not a single DBH reading. If it forks above breast height, measure the single stem as normal — that's a codominant stem structure, not a multi-stem tree, and it gets flagged as a note rather than a separate measurement.

A DBH tape (sometimes called a diameter tape) wraps around the stem like a normal tape but the markings are already divided by π, so the number you read off is the diameter, not the circumference. Wrap a regular tape measure around the same stem and you'll need to divide that reading by π (3.14159) yourself to get diameter — easy to forget in the field, and the source of a lot of DBH numbers that are quietly wrong by a factor of pi.

A multi-stem tree doesn't get one averaged DBH — record each stem's diameter separately at breast height, then list them together (for example "24, 18, 12" cm). Averaging or summing the stems throws away information a client or planning authority may specifically need, particularly for BS5837 category and root protection area calculations, which use an aggregate diameter derived from all stems, not a simple average.

This is exactly how LogLog stores it: DBH is a text field rather than a strict number, specifically so a multi-stem reading can be typed as a comma-separated list without breaking the data model, and each stem also gets its own condition and notes if you need that level of detail.

DBH is one of the handful of fields that shows up on almost every tree record regardless of survey type — species, DBH, and condition are the minimum most clients expect. See the tree inventory guide for the full list of fields worth recording, or how LogLog handles tree data entry in the field, multi-stem included.