Choosing Appropriate Units of Measure

You may have noticed that different things are measured in different units -- even if they involve the same qualities. For example, a can of soda and a lake both contain water.. but it wouldn't make sense to measure a late in milliliters -- just like it wouldn't make sense to measure a can of soda in gallons. We'd be left with either a very large number or a very small decimal number. This is one example of why it's always important to choose the right units of measurement for our experiments and observations.

A review of units of measurement

One of the most important things to understand about units of measurement is that there are two main systems:

• The Imperial System: Also sometimes called "U. S. customary measurements" the Imperial system contains units like quarts, inches, and miles. Its primary use is that it tends to make dealing with fractions easier, for example, 1/3rd of a foot is 4 inches, whereas 1/3d of a meter is 33.33333... cm
• The Metric System: The metric system is used by most countries and is the universal standard for scientists worldwide. It includes units such as meters, liters, and grams. Using the metric system allows for easy communication and understanding of experimental results across different countries and cultures.

A number of different qualities can be measured with both metric and Imperial systems:

• Time: We measure time with seconds, minutes, hours, days, months, years, and centuries. These are the same units for both metric and Imperial systems.
• Distance: The metric system measures distance in meters. Variations include the millimeter, the centimeter, the kilometer, and many others. The Imperial system measures distance in inches, feet, yards, and miles.
• Mass: The metric system measures mass in grams. Variations include milligrams, kilograms, and metric tons. The Imperial system measures mass in ounces, pounds, and tons.

There are many other qualities that we can measure, including frequency, volume, and temperature.

The metric system is easy to understand because it operates based on powers of ten. For example:

• A kilometer is 1000 meters
• A meter is 100 centimeters
• A centimeter is 10 millimeters

With a cursory understanding of Latin, we can also predict the value of any measurement within the metric system:

• "Deca" is a Latin prefix that means "ten"
• "Milli" is a Latin prefix that means "thousand"
• "Centi" is a Latin prefix that means "hundred"

Therefore, a decameter is ten meters, a meter contains a thousand millimeters, and a meter also contains 100 centimeters.

Why is it so important to choose appropriate units of measurement?

Choosing the right unit of measurement is important. When it comes to the specific system of measurement, we don't really have a choice -- since our country makes that decision on our behalf!

But we can choose the appropriate unit.

Here are a few examples:

• If we wanted to measure the distance between two cities, we would use miles or kilometers.
• If we wanted to measure someone's height, we would use feet or meters.
• If we wanted to measure someone's weight, we would use pounds or kilograms.
• If we wanted to measure the capacity of a soda can, we would use milliliters or ounces.
• If we wanted to measure the height of a beetle, we would use inches or millimeters.
• If we wanted to measure the time it takes to drive between two cities, we would use hours.
• If we wanted to measure the amount of time it takes to run 100 meters, we would use seconds.

Note that it does not make sense to use the wrong units in various situations:

• It doesn't make sense to use millimeters to measure the height of a mountain.
• It doesn't make sense to use seconds to measure the time it takes for a planet to orbit the sun.
• It does make sense to use miles to measure the size of a microchip.

You might have noticed that some units seem well-suited to very specific situations. For example, measuring someone's height by feet and inches is straightforward because it gives us whole numbers. By contrast, the metric system leaves us with values like 1.79 meters. There is also no Imperial value smaller than an inch, which means that we're left with values like 1/16th of an inch when measuring small objects like insects.

Topics related to the Choosing Appropriate Units of Measure

Customary Units

Convert Units of Area and Volume

Comparing Quantities

Flashcards covering the Choosing Appropriate Units of Measure

3rd Grade Math Flashcards

Basic Arithmetic Flashcards

Practice tests covering the Choosing Appropriate Units of Measure

Common Core: 3rd Grade Math Diagnostic Tests

3rd Grade Math Practice Tests

Need more help with units of measurement?

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