Measuring Tree Diameter and Height
John Ball, Ph.D. | Professor & SDSU Extension Forestry Specialist
iGrow.org
Estimating the volume of wood in a tree requires two
basic measurements, the tree’s diameter and height.
Once these two measurements are in hand, volume
can be found through the use of a volume table.
Tree diameter
Tree diameter is measured at 4.5 feet above the
ground. This diameter is sometimes referred to as
diameter breast height or simply dbh.
If the tree has a single trunk, no deformities on the
lower trunk and is on level ground, measuring the
diameter at 4.5 feet above the ground is fairly straight
forward. However, if there are some irregularities, here
are the rules to follow to decide where to measure the
diameter.
Diameter measurement for a:
• Tree on a slope is taken on the uphill side at 4.5
feet;
• Leaning tree is taken along the upper side of a lean
at 4.5 feet on the lean;
• Tree with a deformity at dbh, such as a budge, the
diameter is taken above the deformity;
• Tree that forks at dbh, the diameter is taken just
below the fork;
• Tree that forks below dbh, the diameters are taken
one each fork and these are treated as separate
trees.
A simple means of finding the diameter is by first
measuring the tree’s circumference. This can be
done with a cloth measuring tape wrapped around
the trunk or even wrapping a string around the
trunk and measuring off the point where the string
encircled the trunk with a tape measure on ground.
The diameter can be calculated by dividing the
circumference measurement by 3.14. For example if
the circumference is 2 feet 10 inches, 34 inches, the
diameter is 34/3.14 = 10.8 inches diameter.
A diameter tape is often used to measure tree diam eter
Diameter can also be measured directly by using a
tree caliper or Biltmore stick. These can be purchased
through a number of forestry supply catalogs. A caliper
has a scale bar, usually marked off in inches, with
two arms to place on opposite sides of the trunk.
The diameter read off the scale. Since trees are rarely
round, a more accurate measurement with calipers can
be made by taking two measurements at right angles
to one another and averaging the two.
Db h i s t a k e n o n
Db h is t a k e n
Db h is tak en on
the u p p e r s i d e o f
b e lo w t h e f o rk if
b o t h st ems if the
Tree diameter can be determined by wrapping a str ing ar ound
a lean at 4.5 feet
t h e t re e f o rks a t
t re e f o rks below
the tree and then measuring the length of the string with a
4 .5 f e e t
4 .5 f e e t
tape measure
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above the ground. The height is taken by reading off
the scale along the stick. Most hypsometers measure
height in logs in 16-foot increments. A cruiser stick has
both a Biltmore and hypsometer scales.
Tr e e d i a me t e r c a n b e me a su re d w it h a ca lip e r
A Biltmore stick is a straight stick graduated for direct
measurement of dbh. The stick is held horizontally
against the trunk but at 25 inches from the eye. One
end of the stick is lined up with the trunk’s edge and
the other edge of the trunk is used for the diameter.
A hypsometer is used to measure tree height.
Merchantable height
Rarely do we need to determine total height of the
tree. Only when we are felling the tree and need to
know the distance of fall is the total height of interest.
Generally we need to know the merchantable tree
height, the height of the top of the useable portion
of the trunk. The height is either based on a minimal
top diameter; 10 inches for sawlogs, 5 inches for
pulpwood; or to a defect.
Tr e e d i a me t e r c a n b e me a su re d w it h a ca lip e r
Tree height
Tree height can be estimated by a stick that is held at
arm’s length to the eye. Rotate the stick from the eye
to a vertical position while holding it at arm’s length.
Face towards the tree and hold the stick so your fist is
about 1 foot from the base of the tree. When the top of
the stick is even with the top of the tree, the distance
on the ground between you and the tree is equal to
this height. Running a tape from the trunk to this point
will give the height. This works best if the tree has less
than a 5% lean.
A hypsometer can also be used to determine tree
height. This is a straight stick graduated for direct
measurement of height. The user stands 66 feet away
from the tree and holds the stick in a vertical position,
matching the base of the stick to a spot about 1 foot
Merchantable height is to a minimal top diameter o r to a
defect
Defects, irregularities in the log, will usually determine
the merchantable height for sawlogs. The height of a
sawlog is where the tree forks, the first branch occurs
or a crook. Sawlogs are generally measure to 12 or 16
foot lengths though high-value woods such as walnut
may be measured in bolts, 8-foot lengths.
Publication supported in part through the South Dakota Department of Agriculture Division of Resource
Conservation and Forestry.
South Dakota State University, South Dakota counties, and USDA cooperating. South Dakota State University adheres to AA/EEO guidelines
in offering educational programs and services.
Publication: 06-1001-2016
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iGrow.org | A Service of SDSU Extension | © 2016, South Dakota Board of Regents