akar.earthDBH: Definition
What is DBH (diameter at breast height)? How it is measured at 1.3 m, special cases like buttresses and stilt roots, and its role in forest carbon.
DBH (diameter at breast height) is the diameter of a tree stem measured at a standard height, 1.3 m above the ground in most of the world. It is the single most important field measurement in forest carbon accounting because it drives almost every biomass equation.
Why it matters
Biomass rises steeply with diameter, roughly with its square or more. A 1 cm error on a large tree shifts its biomass estimate noticeably, and systematic errors across thousands of trees bias credit volumes. Allometric equations and basal area both start from DBH, so verifiers re-measure a sample of trees to check it.
How it is measured
- Tools: a diameter tape (reads diameter directly from circumference), calipers, or increasingly mobile apps and lidar-equipped phones that estimate diameter from images or point clouds.
- Position: 1.3 m above ground on the uphill side; mark the point with paint or a tag for re-measurement.
- Special cases: for buttresses, measure above them; for forked trees below 1.3 m, measure each stem; for leaning trees, measure along the stem.
- Thresholds: plots set a minimum DBH (for example 5 or 10 cm) and use nested subplots for smaller trees.
Our guides to mobile tree measurement and plot sampling design cover field protocols.
Indonesia angle
Indonesian forests are full of special cases. Dipterocarps develop large buttresses, mangroves such as Rhizophora have stilt roots (measure about 30 cm above the highest prop root), and smallholder coffee and cocoa are often pruned and multi-stemmed. Young ARR seedlings may be below breast height for the first years, so projects record root-collar diameter and height instead.
Common mistakes
- Measuring at different heights in successive campaigns, which creates false growth or shrinkage.
- Wrapping a tape over vines, moss or loose bark.
- Not recording measurement height for irregular stems.
- Mixing circumference and diameter in the same dataset.
Related terms
DBH links to basal area, allometric equation and above-ground biomass. See the ARR hub for how field data becomes credits.
Frequently asked questions
At what height is DBH measured?
The international convention is 1.3 m above the ground on the uphill side of the tree. Some countries use 1.37 m (4.5 feet), so always state the height used.
How do you measure DBH on a buttressed tree?
Measure about 30 cm above the top of the buttress or other deformity, and record the measurement height so the same point is used at re-measurement.