A caliper log provides a representation of the diameter of a borehole along its depth. Wellbores are usually irregular in diameter, it is important to have a tool such as the caliper log that measures diameter at multiple locations.
The drilling engineer will use the caliper measurement as a qualitative indication of both the condition of the wellbore and the degree to which the mud system has maintained hole stability. This is also critical information when calculating the cement volume when the casing is cemented.
Caliper logs can also give some indication of formation types and whether or not the rocks are hard and compact or loose gravel.