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05 September 2003

Measuring with Calipers

Source: Mechanical Engineering Dept., MIT

The figure below depicts a caliper. It can measure lengths from 0 to 7.5 inches to a precision of one thousandth of an inch. One can measure the outside of a part with the jaws, the inside of a hole or slot with the nibs, or the depth of a hole or shoulder with the extension bar.

This particular one is has a vernier scale. It takes a little practice to read it properly. Calipers often have a dial or digital readouts instead.

 

A Vernier Caliper. Click image to enlarge

To read a vernier caliper:

• Read the large number division first.
  
• Read the small number division.
• Read the number of smaller subdivisions. Each represents 0.025 inches to be added to the measurement.
• Read which line on the vernier lines up with a line on the main beam. For each line a thousandth must be added to the measurement.

An example follows:

Click image to enlarge