Metric units of measurement

Here you will learn about metric units of measurement. You will look at common units of measurement in the metric system of measurement and learn about their relative sizes.

Students will first learn about metric units of measurement as part of measurement and data in 4 th grade.

What are metric units of measurement?

Metric units of measurement are the international system of units (SI units) and include the standard units of length (meter), mass (gram), capacity (liter) and time (second).

The metric system is based on powers of 10 (the decimal system). The metric prefixes along with the basic unit vocabulary help identify their standard unit and size.

The prefix “milli” means \cfrac{1}{1000} \, th.

For example,

A millimeter is \cfrac{1}{1000} \, th of a meter.

A milliliter is \cfrac{1}{1000} \, th of a liter.

The prefix “centi” means \cfrac{1}{100} \, th.

For example,

A centimeter is \cfrac{1}{100} \, th of a meter.

A centiliter is \cfrac{1}{100} \, th of a liter.

The prefix “deci,” “deca,” or “deka” means \cfrac{1}{10} \, th.

For example,

A decimeter is \cfrac{1}{10} \, th of a meter.

A decigram is \cfrac{1}{10} \, th of a gram.

The prefix “kilo” means 1,000 times larger.

For example,

A kilometer is 1,000 times larger than a meter.

A kilogram is 1,000 times larger than a gram.

Relative sizes for metric unit measurements

Since there are many different units for measuring, it is helpful to think about each unit in relation to something in the real world. Let’s look at some common units and their relative sizes.

One way to measure an object is length – the distance from one point to another. In the metric system, a meter is the base unit for length.

One way to measure an object is mass – the weight of an object. In the metric system, a gram is the base unit for mass.

Note: A tonne is also referred to as a metric ton, but is NOT the same as a customary ton (2,000 pounds ).

One way to measure an object is capacity – how much space something takes up. In the metric system, a liter is the base unit for capacity (also referred to as the base unit of volume).

One way to measure an event is time – the length of an event with a clear starting and ending moment. In the metric system, a second is the base unit for time.

Note: All of these time measurements are very small, and it can be harder to tell the difference between them on our own.

What are metric units of measurement?

Common Core State Standards

How does this relate to 4 th grade math?

• Grade 4 – Measurement and Data (4.MD.A.1)
  Know relative sizes of measurement units within one system of units including km, m, cm; kg, g; lb, oz.; l, ml; hr, min, sec. Within a single system of measurement, express measurements in a larger unit in terms of a smaller unit. Record measurement equivalents in a two-column table.
  
  For example, know that 1{~ft} is 12 times as long as 1 {~in}. Express the length of a 4{~ft} snake as 48{~in}. Generate a conversion table for feet and inches listing the number pairs (1, 12), (2, 24), (3, 36), …

How to choose a metric unit of measurement

In order to choose a metric unit of measurement:

1. Decide if the measurement is length, mass, capacity or time.
2. Consider the size.
3. Write down the most reasonable choice.

Metric units of measurements examples

Example 1: units of length

What are the most appropriate units to measure the width of a hand-held calculator?

1. Decide if the measurement is length, mass, capacity or time.

Width is a measurement of length, so you need to consider the measurement units based on the meter (m).

2Consider the size.

Thinking about the size of a hand-held calculator, a meter (about the length of a baseball bat) is too large, or a unit and millimeters (about the width of the tip of a pencil) are too small.

3Write down the most reasonable choice.

Centimeters (each about the width of a fingernail) is the most appropriate unit to measure the width of a hand-held calculator.

Example 2: units of length

What are the most appropriate units to measure the distance between London and Paris?

Consider the size.

A meter is about the length from the tips of your fingers when you spread your arms out wide.

The distance from these two cities, which are not in the same country, is much greater than a meter (m).

Example 3: units of mass

What are the most appropriate units to measure the weight of a large dog?

Example 4: units of mass

What are the most appropriate units to measure the weight of a pencil?

Example 5: units of capacity (volume)

What are the most appropriate units to measure the amount of tea in a tea cup?

Example 6: units of capacity (volume)

What are the most appropriate units to measure the amount of water in a pond?

Teaching tips for metric units of measurement

• Worksheets can be helpful for this skill, but not before students have real life experiences with the different metric units. It is much easier to understand metric units if their use is connected to a memory or experience.

• Putting up a “units of the metric system” poster in the classroom can be helpful for students to reference as they are learning the different types of measurements. Particularly if they are used to using the customary system and have less exposure to the metric system.

• This skill should be taught before metric conversions (unit conversions). Once students have experience using metric units and understand their relative size, they are ready to start converting units.

Easy mistakes to make

• Confusing metric and customary units
  A common error is to confuse metric units with customary units of measurement. There are conversion rates between them, but they are different units in different systems.
  For example,
  1{~inch} ≈ 2.5{~cm}
  1{~foot} ≈ 30{~cm}
  1{~mile} ≈ 1.5{~km}

• Thinking the amount of substance changes when a measurement is converted
  When a measurement is converted to another unit, the number representing it becomes smaller or larger. This is not because the amount being measured changed, but the way it was being measured changed.
  For example,
  \$1 = 20 nickels
  Converting \$1 to 20 nickels, increases the 1 to a 20, but since nickels are a smaller unit the overall value of \$1 has not changed. The conversion just shows that it takes 20 nickels to equal \$1.

• Thinking the millionth is the smallest unit in the metric system
  While this unit is very, very small, there are other units even smaller. Because the conversion factors in the metric system are based on the decimal system, and the decimal system goes on forever (decreasing by powers of 10 infinitely), in theory there is no end to the units that can be measured in the metric system.
  The metrics units that currently exist are based off the tools we have available to measure – smaller and smaller units often need more sophisticated measuring tools.

• Forgetting about less common units
  There are units that are commonly used in daily life, like liter and milliliter. But there are also units that exist between (or above and below) these commonly used units. They are easy to forget since they are not used often.
  For example,
  Between liter and milliliter are units between deciliter and centiliter.
  
  

  

  Deciliters are 10 times smaller than liters. And centiliters are 10 times smaller than deciliters.

Related units of measurement lessons

• Units of measurement
• Converting metric units
• Converting units of time
• Conversion of measurement units

The next lessons are

• Represent and interpret data
• Ratio
• Proportion

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