A caliper measures much more accurately than a ruler or folding rule. You can measure thicknesses, distances, and internal and external diameters to tenths of millimeters. But to ensure this precision, you need to know how to work with it. Here, we explain how to use and read different caliper types correctly.

Analogue or Digital Readout

Calipers are divided into two types: digital and analogue. Digital calipers have the advantage of quick and easy reading. They are usually more expensive than analogue calipers.

A caliper consists of the following parts:

man measuring with a digital caliper

Two jaws. The larger one is used to measure the external dimension of an object. The smaller is for measuring the internal dimension.

A vernier scale — a small auxiliary scale — when coupled with the main scale, becomes mobile, allowing measurement to fractions of millimeters or inches.

A thin protruding probe at the back of the ruler. This probe can be used to measure the depth of a hole or recess.

A locking mechanism that must be pushed in to move the caliper or a set screw that can be tightened and loosened.

Digital calipers often do not have a vernier scale but display the exact distance on the screen. It is crucial to realize that you can zero the digital caliper at any position. If you accidentally zero it at 10 mm and move it further, then 9.55 is not 9.55 but 19.55. Ensure that the reading is at 0 when the jaws are completely closed.

Accurately Measuring with a Caliper

Whether you are using an analogue or a digital caliper, these things are important for obtaining a precise measurement:

  • Ensure that the object you want to measure is clean. Since a caliper works so accurately, the smallest speck directly influences the measured value. The caliper itself must also be undamaged and clean.
  • Do not apply pressure to the caliper. The jaws should just touch the material. With soft materials such as wood, you can damage the material by opening the caliper too wide, making the measurement less accurate.
  • When measuring a round object, it is wise to measure at multiple points, making the measurement more reliable.
  • Depth can be measured with the probe. Ensure that it remains straight during measurement. If you exert pressure, the probe can bend, making the measurement less accurate.
  • Measure as much as possible at the end of the jaws for an accurate result.