Diameter tape
![Measurement of tree diameter at breast height, making sure that the tape is perfectly level and that the tape is not kinked, so as not to skew the reading of the diameter.](/Images/godic/202501/08/Using_a_DTApe0920.JPG")
A diameter tape (D-tape) is a measuring tape used to estimate the diameter of a cylinder object, typically the stem of a tree or pipe. A diameter tape has either metric or imperial measurements reduced by the value of pi. This means the tape measures the diameter of the object. It is assumed that the cylinder object is a perfect circle. The diameter tape provides an approximation of diameter; most commonly used in dendrometry.