body{margin:0;} noscript{z-index: 10000; position: fixed; display: block; height: 100%; width: 100%; background: #fff;} noscript .fa{font-size: 40px; display:block; color: #daa520;} noscript div{margin-top: 6%; padding-left: 20px; padding-right: 20px; text-align: center;} ! You must have JavaScript enabled to use this site.

Recommended

Tests

An error ocurred, try again later!

eCourses /

Pre-Algebra /

Chapter {{ article.chapter.number }}

{{ article.number }}.

Show less Show more

Lesson Settings & Tools

	{{ 'ml-lesson-number-slides' \| message : article.intro.bblockCount }}
	{{ 'ml-lesson-number-exercises' \| message : article.intro.exerciseCount }}
	{{ 'ml-lesson-time-estimation' \| message }}

Image Credits

{{ item.file.title }}
{{ presentation }}

No file copyrights entries found

Measuring is the process of using numbers to describe the physical properties of an object or space. Various units are used to measure. For example, many countries measure distance in kilometers, whereas others measure in miles. Converting these units to one another clears this difference. This lesson will teach how to convert measurement units.

Catch-Up and Review

Here are a few recommended readings before getting started with this lesson.

Challenge

Different Measures: Comparing Average Speeds

Two student-led teams, one from Canada and the other the US, made remote controlled robotic cars. Ignacio, of the US, controls the his team's car — Hyperion. Emily, of Canada, controls her team's car — Photon. They are both participating in an international competition and are now doing a test run at the competition site.

Two concept robotic cars being driven by Ignacio and Emily

Ignacio races the robotic car as fast as he can through classrooms, the mountain, around the lake, and finally finishes at the Theatre. Emily's follows a similar path but spends more time going through the mountains. How cool!

Map of the campus where Emily and Ignacio drove their robotic cars

Ignacio's robotic car, Hyperion, traveled $0.4$ miles in $2$ hours. Emily's robotic car, Photon, traveled at an average speed of $0.4$ kilometers per hour. Which robotic car drove at a higher average speed?

Discussion

Unit Ratio

A unit ratio is a ratio with a denominator of

1

unit. Every ratio can be rewritten as a unit ratio.

A ratio is a comparison of two quantities with similar units of measure. Consider writing unit ratios using the relationship between some units of measure. Notice that the denominator of each unit ratio is

1

unit.

The ratio

\frac{1 2 in .}{1 ft},

for example, can be reduced by changing the numerator to

1

foot. The ratio then becomes

\frac{1 ft}{1 ft} .

The units are omitted once they are the same. As a result, the ratio is reduced to

1 .

Also, note that different ratios can be written using the same relationships.

Fact	$1$ $foot$ is equal to $12$ $inches .$	$1$ $hour$ is equal to $60$ $minutes .$
Ratio	$\frac{1 ft}{1 2 in .}$	$\frac{1 h}{6 0 min}$

The denominators of these ratios are different than

1

unit. Divide both the numerator and denominator of each ratio by the number in the denominator. Then, the denominators will be equal to

1

unit.

These resulting unit ratios mean that

1

inch is approximately

0.083

feet and

1

minute is approximately

0.017

hours. Unit ratios are useful when converting measurement units.

Pop Quiz

Practice Rewriting Ratios

Write the given ratio in the indicated form.

Example

Converting the Map's Distance to the Actual Distance

Ignacio relies on a GPS screen to help navigate his robotic car Hyperion through the school's diverse terrain.

Notice the sign on the map's bottom right corner. This means that

1

inch on the map corresponds to

0.075

miles of actual distance at the school. How many miles does

1.4

inches on the map represent in reality? Round the answer to three decimal places if necessary.

Hint

Write a ratio using the fact that $1$ inch on the map represents $0.075$ miles in real distance.

Solution

The goal is to find how many miles

1.4

inches on the map represents in reality. This requires multiplying

1.4

of an inch by a factor that converts inches to miles. Consider the given information on the map.

On the Map 1 in . = In Actual Distance 0.075 mi

Write a ratio using this information. Since the given distance

1.4

is in inches and the goal is to convert it to miles, the denominator of the factor should also be in inches. Doing this ensures that the inches will cancel out. The numerator should contain the needed unit, which is miles.

1 in . = 0.075 mi ⇓ \frac{0 . 0 7 5 mi}{1 in .}

Now multiply

1.4

inches by this ratio to get the distance in miles.

1.4 in . \times \frac{0 . 0 7 5 mi}{1 in .}

MoveLeftFacToNum

$a \cdot \frac{b}{c} = \frac{a \cdot b}{c}$

\frac{1 . 4 in . \times 0 . 0 7 5 mi}{1 in .}

Cross out common units

\frac{1 . 4 in . \times 0 . 0 7 5 mi}{1 in .}

Cancel out common units

\frac{1 . 4 \times 0 . 0 7 5 mi}{1}

Multiply

\frac{0 . 1 0 5 mi}{1}

DivByOne

$\frac{a}{1} = a$

0.105 mi

This means that

1.4

inches on the map represent

0.105

miles in real life.

Discussion

Conversion Factor

A conversion factor is a fraction where the numerator and denominator represent the same quantity with different units.

Example Conversion Factor \frac{6 0 minutes}{1 hour}

Recall that

1

hour and

60

minutes represent the same quantity. Multiplying a quantity by a conversion factor changes the quantity to an equivalent quantity in different units. Examine how to convert

2

hours to minutes using the above conversion factor.

Given Quantity	Conversion	Result
$2$ $hours$	$2 hours \cdot \frac{6 0 minutes}{1 hour}$	$120$ $minutes$

Although the final result is in minutes, both quantities represent the same amount of time. Note that the opposite conversion, from minutes to hours, has a conversion factor of $\frac{1 hour}{6 0 minutes} .$ If the task was to convert $120$ minutes to hours, $120$ minutes would be multiplied by this conversion factor.

Given Quantity	Conversion	Result
$120$ $hours$	$120 minutes \cdot \frac{1 hour}{6 0 minutes}$	$2$ $hours$

As shown in the examples above, the process of including units of measurement as factors is called dimensional analysis. Dimensional analysis can also be used when deciding which conversion factor will produce the desired units. In the table, some common conversion factors are used to convert the given measures.

Given Quantity	Conversion	Result
$3$ $pounds$	$3 pounds \cdot \frac{1 6 ounces}{1 pound}$	$48$ $ounces$
$160$ $ounces$	$160 ounces \cdot \frac{1 pound}{1 6 ounces}$	$10$ $pounds$
$1$ $mile$	$1 mile \cdot \frac{1 7 6 0 yards}{1 mile}$	$1760$ $yards$

Some common conversions involve distance, mass, area, volume, time, and temperature.

Why

The Reason That the Quantities Are Equivalent

The numerator and denominator of the conversion factor represent the same quantity. That means their quotient equals $1 .$ Then, by the Identity Property of Multiplication, the amount of the given quantity does not change when multiplied by the conversion factor.

When converting from one unit to another, the desired unit needs to be in the numerator of the conversion factor while the given unit needs to be in the denominator. That way when the quantity is multiplied by the conversion factor, the given unit will cancel out and the desired unit will remain.

Keep in mind that, despite the given quantity and the new quantity have different values, they represent the same amount.

Discussion

Customary System

The customary system is the system of measurement commonly used in the United States. This system of measurement contains units for length, capacity, and weight. For example, the inch is a unit of length, the ounce is a unit of weight, and the quart is a unit of volume.

Examples of Units in the Customary System inch, ounce, and quart

The table shows the relationship between units of each measure type in the customary system.

Customary Units
Type	Unit	Equivalent Unit
Length	$1$ foot (ft)	$12$ inches (in.)
	$1$ yard (yd)	$3$ feet
	$1$ mile (mi)	$5280$ feet
Weight	$1$ pound (lb)	$16$ ounces (oz)
Weight	$1$ ton (T)	$2000$ pounds
Volume	$1$ cup (c)	$8$ fluid ounces (fl oz)
	$1$ pint (pt)	$2$ cups
	$1$ quart (qt)	$2$ pints
	$1$ gallon (gal)	$4$ quarts

Converting measures requires using the appropriate conversion factors.

Example

Determining the Weight of the Robotic Car

The robotics competition that each team will join requires that the robotic cars weigh less than $6$ pounds. The robotic car designed by Ignacio's team, Hyperion, currently weighs $84$ ounces.

a Find the weight of the robotic car in pounds.

b Does the weight of this robotic car meet the requirement?

Hint

a Write a conversion factor using the fact that

1

pound is

16

ounces.

b Compare the answer from Part A with

6

pounds.

Solution

a A conversion factor is needed to convert the given quantity from ounces to pounds. Recall how pounds and ounces are related.

1 pound is 16 ounces . or 1 lb = 16 oz

Because the required unit is

pounds,

it will be written in the numerator of the conversion factor. The unit in the denominator will be the same as the unit of the given amount,

ounces,

allowing them to cancel out.

Conversion Factor Ounces \to Pounds \frac{1 lb}{1 6 oz}

Now convert the given quantity in ounces to pounds by multiplying

84

ounces by the conversion factor.

84 oz \cdot \frac{1 lb}{1 6 oz}

MoveLeftFacToNum

$a \cdot \frac{b}{c} = \frac{a \cdot b}{c}$

\frac{8 4 oz \cdot 1 lb}{1 6 oz}

Cross out common units

\frac{8 4 oz \cdot 1 lb}{1 6 oz}

Cancel out common units

\frac{8 4 \cdot 1 lb}{1 6}

MultByOne

$a \cdot 1 = a$

\frac{8 4 lb}{1 6}

MovePartNumRight

$\frac{a \cdot b}{c} = \frac{a}{c} \cdot b$

\frac{8 4}{1 6} lb

CalcQuot

Calculate quotient

5.25 lb

Therefore, the robotic car is

5.25

pounds.

b In Part A, the weight of the robotic car was found. It is equal to

5.25

pounds, which is less than

6

pounds.

5.25 lb < 6 lb

This means that Ignacio's team is eligible to participate in the event.

Discussion

Metric System

The metric system is the system of measurement used in almost all countries. The base units in the metric system are meters for length, liters for capacity, and grams for weight.

Base Units in Metric System meter, liter, and gram

In the metric system, multiples of units follow a decimal pattern. That is, they are powers of

10 .

Other metric units are named by adding metric prefixes to the base units.

Metric Units of Length

The table shows the commonly used metric units of length.

Unit	Equivalent Unit
$1000$ millimeters (mm)	$1$ meter (m)
$100$ centimeters (cm)	$1$ meter
$10$ decimeters (dm)	$1$ meter
$1$ dekameter (dam)	$10$ meters
$1$ hectometer (hm)	$100$ meters
$1$ kilometer (km)	$1000$ meters

Metric Units of Capacity

For measuring capacity, the metric system uses the liter as the base unit.

Unit	Equivalent Unit
$1000$ milliliters (mL)	$1$ liter (L)
$100$ centiliters (cL)	$1$ liter
$10$ deciliters (dL)	$1$ liter
$1$ dekaliter (daL)	$10$ liters
$1$ hectoliter (hL)	$100$ liters
$1$ kiloliter (kL)	$1000$ liters

Metric Units of Weight

In the metric system, kilogram, gram, and milligram are some commonly used units for measuring weight.

Unit	Equivalent Unit
$1000$ milligrams (mg)	$1$ gram (g)
$100$ centigrams (cg)	$1$ gram
$10$ decigrams (dg)	$1$ gram
$1$ dekagram (dag)	$10$ grams
$1$ hectogram (hg)	$100$ grams
$1$ kilogram (kg)	$1000$ grams

Note that each relationship in the tables can be written as a ratio. These ratios can be considered as conversion factors.

Example

The Length of the Robot Car Designed by Emily’s Team

Ignacio's team discovered that their robotic car met the weight criteria. At the same time, Emily's team was putting another criterion to the test. The length criterion requires that the cars are no longer than $40$ centimeters.

a Photon, Emily's team's robotic car, is

0.35

meters long. Write this length in centimeters.

b Does this car meet the length criteria?

Hint

a Write a conversion factor using the fact that

1

meter is

100

centimeters.

b Compare the answer from Part A with

40

centimeters.

Solution

a The given length is in meters. To convert from meters to centimeters, use the fact that

1

meter is

100

centimeters.

1 meter is 100 centimeters . or 1 m = 100 cm

In this case, the required unit is

centimeters,

so it will be in the numerator of the conversion factor. The denominator will be its equivalent in

meters

so that meters are canceled out when multiplied by

0.35

meters.

Conversion Factor Meters \to Centimeters \frac{1 0 0 cm}{1 m}

Now convert the given quantity from meters to centimeters by multiplying it by the conversion factor.

0.35 m \cdot \frac{1 0 0 cm}{1 m}

MoveLeftFacToNum

$a \cdot \frac{b}{c} = \frac{a \cdot b}{c}$

\frac{0 . 3 5 m \cdot 1 0 0 cm}{1 m}

Cross out common units

\frac{0 . 3 5 m \cdot 1 0 0 cm}{1 m}

Cancel out common units

\frac{0 . 3 5 \cdot 1 0 0 cm}{1}

DivByOne

$\frac{a}{1} = a$

0.35 \cdot 100 cm

Multiply

35 cm

The length of the car is

35

centimeters.

b The car has a length of

35

centimeters. This is less than

40

centimeters.

35 cm < 40 cm

It follows that Photon meets this criteria.

Discussion

Converting Measures Between Systems

Units in the customary system can be converted to units in the metric system and vice versa. This may necessitate recalling a lengthy list of conversion factors.

Conversion factors between different units of measurement

Example

Filling Out the Competition Application

Emily and Ignacio are filling out the application form for the robotics competition. They must enter the measurements of their cars in multiple system's units.

Applications
Name of Robotic Car	Weight		Length
Hyperion	$5.25$ pounds	$A$ kilograms	$15$ inches	$B$ centimeters
Photon	$C$ pounds	$2.5$ kilograms	$D$ inches	$35$ centimeters

Help them find the equivalent measurements. If necessary, round answers to two decimal places.

Hint

Remember, $1$ kilogram is about $2.2$ pounds and $1$ inch is $2.54$ centimeters.

Solution

Notice that Hyperion's known measurements are in customary units, whereas Photon's known measurements are in metric units. Conversion between the systems is needed. The equivalent weights will be found first followed by the equivalent lengths.

Finding Missing Equivalents of Weights

The weights are in kilograms and pounds. Recall the relationship between these units.

1 kilogram is about 2.2 pounds . or 1 kg \approx 2.2 lb

The required conversion factor will be obtained using this information.

Finding A

The weight of Hyperion is

5.25

pounds. In this case, the conversion factor should have a numerator in kilograms and a denominator in pounds.

Conversion Factor Pounds \to Kilograms \frac{1 kg}{2 . 2 lb}

After determining the factor, multiply the weight of Hyperion and the conversion factor.

5.25 lb \cdot \frac{1 kg}{2 . 2 lb}

MoveLeftFacToNum

$a \cdot \frac{b}{c} = \frac{a \cdot b}{c}$

\frac{5 . 2 5 lb \cdot 1 kg}{2 . 2 lb}

Cross out common units

\frac{5 . 2 5 lb \cdot 1 kg}{2 . 2 lb}

Cancel out common units

\frac{5 . 2 5 \cdot 1 kg}{2 . 2}

MultByOne

$a \cdot 1 = a$

\frac{5 . 2 5 kg}{2 . 2}

MovePartNumRight

$\frac{a \cdot b}{c} = \frac{a}{c} \cdot b$

\frac{5 . 2 5}{2 . 2} kg

CalcQuot

Calculate quotient

2.386363 \dots kg

RoundDec

Round to $2$ decimal place(s)

\approx 2.39

Hyperion has a weight of about

2.39

kilograms. In other words, the value of A is

2.39 .

Finding C

To find the weight of Photon in pounds, the multiplicative inverse of the above conversion factor is needed. This is because the measurement in kilograms is converted to pounds.

Conversion Factor Kilograms \to Pounds \frac{2 . 2 lb}{1 kg}

Use this factor to find the equivalent weight in pounds.

2.5 kg \cdot \frac{2 . 2 lb}{1 kg}

MoveLeftFacToNum

$a \cdot \frac{b}{c} = \frac{a \cdot b}{c}$

\frac{2 . 5 kg \cdot 2 . 2 lb}{1 kg}

Cross out common units

\frac{2 . 5 kg \cdot 2 . 2 lb}{1 kg}

Cancel out common units

\frac{2 . 5 \cdot 2 . 2 lb}{1}

DivByOne

$\frac{a}{1} = a$

2.5 \cdot 2.2 lb

Multiply

5.5 lb

Photon has a weight of

5.5

pounds. The value of C is

5.5 .

Finding Missing Equivalents of Lengths

This part requires converting between inches and centimeters. At this point, it is useful to remember that

1

inch is

2.54

centimeters.

1 inch is 2.54 centimeters . or 1 in . = 2.54 cm

Finding B

The length of Hyperion is

15

inches. The conversion factor of

\frac{2 . 5 4 cm}{1 in .}

will convert this length to centimeters.

Conversion Factor Inches \to Centimeters \frac{2 . 5 4 cm}{1 in .}

Multiply the length of Hyperion by this conversion factor to get the equivalent length in centimeters.

15 in . \cdot \frac{2 . 5 4 cm}{1 in .}

MoveLeftFacToNum

$a \cdot \frac{b}{c} = \frac{a \cdot b}{c}$

\frac{1 5 in . \cdot 2 . 5 4 cm}{1 in .}

Cross out common units

\frac{1 5 in . \cdot 2 . 5 4 cm}{1 in .}

Cancel out common units

\frac{1 5 \cdot 2 . 5 4 cm}{1}

DivByOne

$\frac{a}{1} = a$

15 \cdot 2.54 cm

Multiply

38.1 cm

Hyperion has a length of

38.1

centimeters. The value of B is

38.1 .

Finding D

Finally, Photon's length will be converted to inches. This calls for multiplication by

\frac{1 in .}{2 . 5 4 cm} .

Conversion Factor Centimeters \to Inches \frac{1 in .}{2 . 5 4 cm}

Multiply

35 cm

\frac{1 in .}{2 . 5 4 cm} .

35 cm \cdot \frac{1 in .}{2 . 5 4 cm}

MoveLeftFacToNum

$a \cdot \frac{b}{c} = \frac{a \cdot b}{c}$

\frac{3 5 cm \cdot 1 in .}{2 . 5 4 cm}

Cross out common units

\frac{3 5 cm \cdot 1 in .}{2 . 5 4 cm}

Cancel out common units

\frac{3 5 \cdot 1 in .}{2 . 5 4}

MultByOne

$a \cdot 1 = a$

\frac{3 5 in .}{2 . 5 4}

MovePartNumRight

$\frac{a \cdot b}{c} = \frac{a}{c} \cdot b$

\frac{3 5}{2 . 5 4} in .

CalcQuot

Calculate quotient

{{ article.displayTitle }}

Catch-Up and Review

Hint

Solution

Why

Hint

Solution

Metric Units of Length

Metric Units of Capacity

Metric Units of Weight

Hint

Solution

Hint

Solution

Finding Missing Equivalents of Weights

Finding A

Finding C

Finding Missing Equivalents of Lengths

Finding B

Finding D