How to Read Metric Rulers

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  • 0:04 Metric Rulers
  • 1:02 Reading a Metric Ruler
  • 2:13 Parallax Error
  • 2:39 Practice Problem
  • 3:16 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Being able to read a metric ruler is an important skill to learn. In this lesson, you'll learn about the three special steps that will make you a ruler-reading expert and solve a real-life practice problem.

Metric Rulers

Making accurate measurements is very important! The first step in measuring the length of an object using a ruler is making sure that you're using the correct ruler. Most rulers have two sides; one side measures distance in inches, and the other in centimeters. If you want to measure something using metric units, be sure to choose the side of the ruler that measures in centimeters (cm).

Sometimes a ruler may clearly indicate which side measures centimeters, but other times you may have to rely on some clues to figure it out. So, how can you tell which side measures in centimeters? There are two things to look for. First, centimeters are smaller than inches, so the side with the smaller increments will be the metric side of the ruler. Second, in the metric system, each unit of measurement can always be divided into 10 smaller units of measurement, so look to see which side has exactly 10 divisions between each number, and that will be the metric side. If you always remember to look for those two things, you can be sure you're using the right part of the ruler

a metric ruler

Reading a Metric Ruler

On a metric ruler, the numbers represent centimeters. The individual lines between the numbers represent millimeters. Each millimeter is one-tenth of a centimeter, so ten millimeters equals one centimeter.

Before you start measuring, make sure that one end of the object is lined up with the 0 cm mark on the ruler. Then look at the other end of the object to measure how long it is. When you record the measurement, you will always record it using 2 decimal places.

If you follow these three simple steps, you can be sure to always measure accurately:

ruler example

  1. Determine the number of centimeters by identifying the number just before the end of the object.
  2. Determine the number of millimeters by counting the number of lines past that number until you get to the end of the object. If the object is in between two lines, use the one before the end of the object. This will tell you how many tenths of a centimeter (or millimeters) you have. This number will go right after the decimal point.
  3. Determine the decimal place. If the object aligns with the millimeter, the second decimal place will be 0. If it falls between two millimeters, the second decimal place will be 5.

Now you're ready to write the measurement, which looks like this:

Example of how to write a measurement

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