How Do You Read a Vernier Caliper?

A Vernier caliper is read by looking at aligned tick marks that read centimeters, millimeters and tenths of a millimeter on a sliding scale, according to the Southern Methodist University Department of Physics. The error of a Vernier caliper is 0.05 millimeters.

A vernier caliper can measure external and internal dimensions, and many measure depth as well. Vernier calipers have a fixed scale and a moving scale in two units: Imperial (inches) and millimeters. Typically the bottom half provides external measurements using a fixed point and a moving second point. Internal dimension points are located on the top half, and the sliding portion often includes a rod for depth measurement. Along the sliding portion are additional scales to help measure fraction or decimals to an accuracy of within 1/128 inch or 0.05 mm.

The main scale of a Vernier caliper is the reading that is to the left of zero on the tenth of a millimeter sliding scale. Then, the next reading is taken by the closest congruent line. If the 0.08 centimeter line is most closely aligned to another line on the scale below it, the final reading includes 0.08 centimeter. The tenth of a millimeter line is read by alignment only, no matter what the millimeter reading is below it. If no line exactly matches up, the closest one is taken, and the reading is then approximated.

One common mistake occurs when someone tries to read the closest line to zero, rather than the one to the left of the zero line. Another possible mistake happens when someone finalizes the tenths of a millimeter mark on a Vernier caliper. These readings are made by rounding to the nearest mark as if there was no such precision with the instrument.

A Vernier caliper measures diameters and widths of objects between two jaws that close tightly on objects. The tighter the calipers, the more precise the measurements.

  1. Determine which units to use

    Imperial units are located on the top half of a vernier caliper, and millimeters on the bottom half. Decide which units you are needing to use.

  2. Determine what type of measurement to take

    For external dimensions, use the points, or jaws, on the lower half and place the object between the jaws. For internal dimensions, use the upper set of jaws, and place the caliper inside the area to be measured, sliding until the jaws cannot move. For depth measurement, use the rod and slide the caliper down until it no longer moves.

  3. Read the vernier scales

    For Imperial units, locate the zero on the sliding scale, and read off units left to right up to the zero. From the zero, read right until one of the tick marks aligns with the tick marks on the fixed scale. The number of tick marks past zero provides the measurement of fractional inches. For metric units, follow the same steps until you get the number of tick marks past zero; this provides the measurement in millimeters up to 0.05mm.