How to Use a Ruler to Measure in Centimeters

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Math and science instructor Jessie Antonellis-John explains how to measure in centimeters

Co-authored by Jessie Antonellis-John and Amy Bobinger, BA

Last Updated: August 4, 2026 Fact Checked

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• Measuring in Centimeters
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• Converting Centimeters, Millimeters, & Meters
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• When to Measure in Centimeters
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• Video

|Show more |Show less

Centimeters are great for measuring small objects—but how do you read them on a ruler? Not to worry! We partnered with a math and science instructor to provide a super-simple step-by-step guide that will make you a centimeter-reading pro in no time. First, we’ll walk you through measuring in centimeters. Then, we’ll go over the difference between centimeters, millimeters, and meters, and how to convert between them. Let’s get started!

How do you read a ruler in centimeters?

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Math and science instructor Jessie Antonellis-John says to line up the 0 mark with the beginning of the length you want to measure, and note the measurement of the end of that length. Each small mark is one-tenth (0.1) of a centimeter, which is equivalent to 1 millimeter.

Steps

Section 1 of 3:

How to Measure in Centimeters on a Ruler

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1. 
   1
   Find the centimeter side of the ruler. Most rulers have inches on one side and centimeters on the other. Look for a label that says “cm”—that will be the centimeter side.

   • If your ruler doesn’t have a label, the centimeters are the side with the smaller units of measurement, and the inches are the side with the larger units.
   • If you’re still not sure, count the hash marks between the whole numbers. If there are ten small marks between the numbers, those are centimeters. If there are 16 marks, that’s the inch side.

   Meet the wikiHow Expert

   Dr. Jessie Antonellis-John is a math and science instructor who teaches at Engaging Math Circles. With over 10 years of experience, she specializes in curriculum development and cultural relevance in STEM.
2. 
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   Line the left side of the object up with the zero mark on the ruler. Line up the 0 mark with the beginning of the length you want to measure, and note the measurement of the end of that length, states Antonellis-John. Be sure the edge of whatever you’re measuring is exactly lined up with the line under the zero on the centimeter ruler. If there isn’t a “0,” use the first printed line on the ruler—not the outside edge of the ruler. If the object isn’t lined up perfectly, your measurement will be off.

   • If the object is too far to the left, your measurement will be too short.
   • If the object is too far to the right, your measurement will be too long.
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3. 
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   Find the closest whole number at or before the end of the object. Now, go to the right side of the object. If the edge of the item lines up with a whole number, you found the answer—that number is how many centimeters long your object measures!

   • If the edge of the object is between two whole numbers, write down the last whole number the object passes. (So if the object goes past 4 but doesn’t touch 5, you’d write down 4.) Then, use the next step to find the rest of the measurement.
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   Count the smaller lines if the measurement isn’t a whole number. To find the exact measurement of your object, count the number of small lines between the whole number and the edge of the object. The larger, numbered markings are centimeters, and the smaller lines indicate millimeters, notes Antonellis-John. Once you’ve counted those, write a “.” (decimal) after the whole number, then write down how many lines you counted.

   • For example, if our object measures 6 small lines past the whole number 4, it would be 4.6 centimeters (cm).
   • As Antonellis-John explains, there are 10 millimeters in a centimeter, so you can easily read off your measurement as a decimal or a fraction. “For instance, if your measurement is 7 centimeters and 3 millimeters, you can write it as 7 3/10 or 7.3.”
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Section 2 of 3:

Converting Centimeters, Millimeters, & Meters

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1. 
   1 meter equals 100 centimeters. The prefix “cent” means 100, so a centimeter is one-hundredth of a meter. In other words, it takes 100 centimeters to make a meter. Similarly, “milli” means thousand, so it takes 1,000 millimeters to equal a meter. Here’s how it all breaks down:

   • Multiply meters by 100 to get centimeters. If you have something that measures 2.3 meters, you can find out how many centimeters that is by multiplying by 100—in this case, that’s 230 centimeters.
   • Divide centimeters by 100 to get meters. Conversely, you can find out how many meters something is by dividing the centimeters by 100. For example, if you measured your height as 162 centimeters, Antonellis-John says you could divide by 100 to convert it to meters: 1.62 meters.
   • Multiply or divide by 1000 to convert between millimeters and meters. Multiply meters by 1000 to find out how many millimeters it is, or divide millimeters by 1000 to find the length in meters. For example, you could convert 1.62 meters into kilometers by dividing by 1000, the number of meters in a kilometer, Antonellis-John explains.
   • Multiply or divide by 10 to convert between millimeters and centimeters. 1 centimeter equals 10 millimeters, so multiply centimeters by 10 to find millimeters, or divide millimeters by 10 to find centimeters.

Section 3 of 3:

When should you measure in centimeters?

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1. 
   Centimeters are best for measuring small objects. One good reason for using centimeters is that they’re slightly smaller than inches, so they’re better for measuring smaller items more precisely, shares Antonellis-John. Since centimeters are smaller than inches, they can help you find precise measurements for small items like coins, paperclips, crayons, blocks, leaves, or flowers. Here are some other reasons you might use centimeters:

   • Go with centimeters when you need your answer in decimals. The small marks between inches are measured in 1/16ths, so the answer is usually given in fraction form. If you need your answer in decimals, it’s better to work with centimeters, since a millimeter is the same as 0.1 (or 1/10th) of a centimeter.
   • Choose metric measurements for a worldwide audience. Aside from the US, most countries use the metric system (centimeters, millimeters, meters, and kilometers). Because centimeters are a metric unit, they convert easily to any other metric unit of length using powers of 10, says Antonellis-John.
   • Use centimeters for science projects. Most scientific measurements are performed using centimeters and millimeters. These measurements are very precise, and they’re easy to use in math equations since you’re working with decimals.
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