Diameter at breast height, or DBH, is a standard method of expressing the
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...
of the
trunk or
bole of a standing
tree
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...
. DBH is one of the most common
dendrometric measurements.

Tree trunks are measured at the height of an adult's breast, which is defined differently in different countries and situations. In many countries, DBH is measured at approximately above ground.
Global variation and scientific precision
The height can make a substantial difference to the measured diameter.
In the United States, DBH is typically measured at above ground.
[
In some countries, such as Australia, New Zealand, Burma, India, Malaysia, and South Africa, breast height diameter has historically been measured at a height of , but because of much active research into allometrics that are being applied to trees and forests, the convention of is more appropriate.] Ornamental trees are usually measured at 1.5 metres above ground.
Some authors have argued that the term DBH should be abolished because the heights at which the diameter is measured are excessively variable and imprecise, and imprecise measurements could strongly influence forestry calculations such as biomass. An alternative proposed by Brokaw and Thompson (2000) is D''x'', whereby the ''x'' indicates the exact height above the floor (and along the stem) at which the diameter is measured, e.g. D''130'' denotes a diameter measured at 130 cm above the ground and along the stem.
On sloping ground, the "above ground" reference point is usually taken as the highest point on the ground touching the trunk, but some use the average between the highest and lowest points of ground. If the DBH point falls on a swelling in the trunk it is customary to measure the girth below the swelling at the point where the diameter is smallest. Other ambiguous settings for determining the exact place where to measure the diameter is given in Dahdouh-Guebas & Koedam (2006).
Methodology
The two most common instruments used to measure DBH are a girthing (or diameter) tape and calipers.
A girthing tape actually measures the girth (circumference
In geometry, the circumference () is the perimeter of a circle or ellipse. The circumference is the arc length of the circle, as if it were opened up and straightened out to a line segment. More generally, the perimeter is the curve length arou ...
) of the tree; the girthing tape is calibrated in divisions of π centimetres (3.14159 cm). The measure assumes the trunk has a circular cross-section and gives a directly converted reading of the diameter. It is accurate for most plantation
Plantations are farms specializing in cash crops, usually mainly planting a single crop, with perhaps ancillary areas for vegetables for eating and so on. Plantations, centered on a plantation house, grow crops including cotton, cannabis, tob ...
trees.
Calipers consist of two parallel arms one of which is fixed and the other able to slide along a scale. Calipers are held at right-angles to the trunk with the arms on either side of the trunk. Precision can be improved on non-circular stems by averaging two caliper measurements taken at right-angles. Electronic calipers are also available enabling highly accurate measurements to be taken and stored for further analysis.
DBH is used in estimating the amount of timber
Lumber is wood that has been processed into uniform and useful sizes (dimensional lumber), including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, window frames). ...
volume in a single tree or stand of trees utilising the allometric correlation between stem diameter, tree height and timber volume.[ It can also be used in the estimation of the age of veteran trees, given that diameter increment is the only "constant non-reversible feature of tree growth".][
]
See also
* The world's stoutest tree species
* Tree measurement
* Biltmore stick
* Crown (botany)
* Forest inventory
* Site index
* Site tree
* Tree crown measurement
References
*
{{DEFAULTSORT:Diameter At Breast Height
Forest modelling
Volume