What Is a Plant Caliper?

Where to Measure Tree Caliper

• Since tree trunks are generally wider at ground level and taper as you rise higher on the trunk, keep the measurement consistent by always measuring 4.5 feet above ground. This standard point of measurement is called breast height. If the tree has swellings, knots or other deformities at breast height, take the measurement just above the deformity. If the tree forks at or below breast height, measure just below the fork.

Measuring Diameter With a Caliper

• A caliper has two arms that slide to the left and right sides of the tree trunk and a scale between the arms where you can read the measurement in inches. Hold the caliper level across the tree at breast height when taking the measurement. Tree trunks aren't perfectly round, so take another measurement at a right angle to the first reading. Average the two measurements by adding them together and dividing by two.

Determining Caliper With a Measuring Tape

• You don't have to have a caliper to measure the diameter of a tree tree trunk. You can accomplish the same thing with a measuring tape and a simple calculation. Wrap the measuring tape around the tree at breast height and note the measurement in inches. Make sure it is level all the way around the tree. This measures the circumference of the tree. Determine the diameter by dividing the circumference by 3.14.

Estimating Caliper With a Biltmore Stick

• A Biltmore stick, which looks like a yard stick but with different increment markings, estimates the caliper of a tree to within 2 inches. To use the stick, stand 25 inches from the tree and place the stick against the tree so that the zero mark lines up with the left edge of the tree in your line of site. Without moving your head, shift your eyes to the right side of the tree and note the number that lines up with the right edge of the trunk. This number is the diameter, or caliper, of the tree.