The Connecticut Botanical Society uses American Forests’ tree measurement system, which produces a single number that we call points. American Forests is responsible for National Register of Big Trees.

The formula simply adds together:
• trunk circumference at 4.5 feet above ground, in inches
• tree height, in feet
• one-quarter of the average canopy spread, in feet.

Circumference.  With a tape measure, find the circumference (not diameter) at 4 feet 6 inches above ground level. If the tree is growing on a slope, measure the 4.5 feet up from the center of the slope, i.e. not the lowest or highest place where ground meets tree. If branches begin to swell the trunk at or below 4.5 feet, measure the smallest circumference below 4.5 feet. If the tree is multiple stemmed and forks above ground level, measure the smallest circumference below the place where the stems originate and also measure each stem at 4.5 feet. If it is multi-stemmed into the ground, measure each stem separately and note this condition on the datasheet. Convert feet and inches to inches for the calculation.

Height.  We do not use estimates for trees which are contenders for largest of their kind. Most of the measurements for this project have been done with a clinometer (available from forestry supply companies) which we find accurate to one or two feet in 100. This device, which currently costs about $150, is held in the hand and the treetop is sighted through it. A scale visible inside gives height in feet when the clinometer is exactly 100 feet from a point directly below the sighted branch (note this is not necessarily the base of the tree trunk). With a simple calculation it can be used at distances other than 100 feet. An estimate can sometimes be done by measuring the tree's shadow, measuring the shadow of an object of known height, and using the difference between the object's true height and shadow length as a correction factor to obtain the tree height. This is usually more accurate than guessing, but only works on sunny days on open sites. There are various other optical and electronic instruments available for measuring heights. Use the height in feet for the calculation.

Average Spread. With two people, or by pinning down one end of the tape, measure the greatest branch spread from one end of the canopy in a straight line next to the trunk to the far edge. In the same way, measure a second spread in a line perpendicular (90 degrees) to the first line, regardless of canopy size above. The two spread measurements, in feet, are averaged and divided by 4 for the AFA points calculation.

For more detailed information, please see this document: American Forests' Tree Measuring Guidelines.


Information about potentially notable trees in Connecticut can be sent to or by mail to:

Notable Trees Committee
Connecticut College Arboretum
270 Mohegan Avenue
New London, CT 06320

Please include the name of the tree if at all possible, the circumference at 4.5 feet above ground, and the name, phone number and address of someone who will show us the tree if we decided it merits a complete measurement.

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