How to Read Decimal Calipers

Caliper measuring scale

Calipers are a form of measurement designed to give accurate results when measuring the inside or outside sides of an object. This measurement is often done to measuring small round objects where traditional measuring might lead to a less-than-exact result.

Instructions

1. Attach the caliper to the object you wish to measure. You will be using the metric system to measure the object since the result will be expressed in a decimal. Measurements in inches are expressed as fractions.

2. Calculate the measurement in whole millimeters by finding the numbered mark to the left of the starting point (the 0) of the movable scale. Write this number down.

3. Determine if the 0 line exactly overlaps a marking on the scale. If this is the case, record the number of millimeters. Next add a decimal point and two 0s to the right of the decimal point. If this is the case, you're finished with the measurement.

4. Find the line on the movable scale that most closely lines up with a line on the fixed scale. If the line on the fixed scale is long, write the number down as a tenth of a millimeter with a 0 in the hundredths place. For example, the reading could be would be written as ".20."

5. Write down a 5 in the hundredths place if the line on the fixed scale is short. For example, the reading might be ".25" if the scale falls after the marking for .2 mm but before the marking for .3 mm.

6. Add the whole millimeter amount you recorded from Step 2 and the measurement determined from Steps 4 and 5. The result is your caliper measurement in decimal form. For example, a whole millimeter measurement of 4 plus the decimal measurement of .15 would yield a measurement of 4.15 mm.

Tips & Warnings

• Some calipers are designed to measure in both inches and millimeters. Know which side of your scale measures in your chosen unit. A more accurate reading can be obtained using a digital caliper that outputs measurements without using an external scale.

References

• University of Toronto Department of Physics