Converting Metric Units of Measure

by Laurie Laurendeau on February 7, 2012

The Metric system is used around the world in most countries.  The U.S. is slowly adopting this system of measurement, and your child is likely learning about the Metric system, as well as U.S. Customary system.  Once your child has had the opportunity to measure various objects using centimeters, millimeters, and meters, she will be ready to begin understanding the relationship between these measures, and how to convert between them.

The Metric system is based on a base-ten system, so each unit of measure is 10 times bigger than the previous unit.  The smallest commonly-used unit in the Metric system is the millimeter (mm).  Here is the order of the Metric units for measuring length from least to greatest:

millimeter (mm)

centimeter (cm)

decimeter (dm)

meter (m)

dekameter (dk)

hectometer (hm)

kilometer (km)

I will now list the units from left to right:

Kilo         hecto    deka      UNIT      deci        centi      milli

I called the middle unit simply “UNIT” because you can use these same prefixes to learn the order of metric units of capacity (liters) and weight (grams).  When you’re measuring length, the “unit” would be the meter.  An easy way to remember the Metric prefixes is with the following sentence:

King Henry Doesn’t  USUALLY Drink Chocolate Milk

The “K” in King Henry stands for kilo, the “H” stands for hecto, the “D” stands for deka, the “U”stands for UNIT (Length: the unit would be meter, Capacity: the unit would be Liter, and Weight: the unit would be Gram), the “D” stands for deci, the “C” stands for centi, and the “M” stands for milli.

So, now that we know the order of the prefixes, we can talk about how to convert between units.  As you move from left to right across the prefixes, it’s 10 times bigger than the previous unit.  For example, if you have 30 centimeters, and you move one spot to the right to millimeters, you will have 10 times more, or 300 millimeters.  Another example:  If you have 45 kilometers, and you move 3 spots to the right to UNIT (meters), you will have 10x10x10 (or 1,000) times your unit.  So, 45 kilometers = 45,000 meters.

Conversely, if you move from right to left, the units are divided by multiples of 10.  For example, if you have 200 centimeters, and you move 2 spots to the left to UNIT (meters), you would do 200 /10 /10 to end up with 2 meters.  This can get a bit trickier when you have small numbers and you are moving to the left.  The reason it is more difficult is because you might move into decimals.  For example, if you begin with 20 millimeters, and you move to kilometers, you would be jumping back 6 spots, or 10/10/10/10/10/10 (or 1,000,000), and you would move the decimal point to the left 6 places, to get an answer of 0.000020 kilometers.  When your child is beginning to convert metric units, try to keep the numbers out of the decimals until she gets the hang of it!

You can use the same prefixes we learned above to convert units of capacity and weight.  Here are the units:


KILOGRAM              Hectogram          Dekagram           GRAM   decigram             centigram            MILLIGRAM


Kiloliter                 Hectoliter            Dekaliter              LITER     deciliter                centiliter              MILLILITER

Please note the units in uppercase letters.  These are the units that we commonly see on packaging and in the world around us.  While the other units are important to know, be sure your child has a good understanding of the most commonly used units.


  • As always, playing math games at home is a great way to reinforce math skills learned in school.
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