Measuring means finding a number that describes the size of something. In particular, we determine how long or short an object is by measuring its length. We use length units to specify an object's length.
The most popular measurement system within the scientific community is the metric system. Within the metric system, the most common units of measurement are called base units.
The base unit of length is the meter, which we denote using the symbol "." Lengths are measured using meter sticks like the one below.
It's convenient to define new units of measurement from the base unit. The most common variations for length units are shown below:
| Name | Symbol | Conversion |
|---|---|---|
| Kilometer | ||
| Meter | Base Unit | |
| Centimeter | ||
| Millimeter |
Let's give some examples of each unit, going from the largest unit to the smallest :
The world's tallest building is the Burj Khalifa in Dubai. Its height is approximately
The length of one large stride is approximately
The width of a standard paperclip is around
The thickness of a credit card is around
Important: Each metric symbol of length ends in "", the base unit.
Suppose we want to measure the length of the Golden Gate Bridge (California, USA). Which of the following metric units could we use?
A table showing the metric units of length is given below.
| Name | Symbol |
|---|---|
| Kilometer | |
| Meter | |
| Centimeter | |
| Millimeter |
Therefore, from the given options, the only unit of length is
Suppose we want to measure the length of a button. Which metric unit could we use?
|
a
|
$\textrm{mm}$ |
|
b
|
$\textrm{kg}$ |
|
c
|
$\textrm{s}$ |
|
d
|
$\textrm{ms}$ |
|
e
|
$\textrm{mg}$ |
Suppose we want to measure the length of Central Park (New York, USA). Which metric unit could we use?
|
a
|
$\textrm{L}$ |
|
b
|
$\textrm{s}$ |
|
c
|
$\textrm{g}$ |
|
d
|
$\textrm{km}$ |
|
e
|
$\textrm{kg}$ |
Let's recall the table that relates metric units of length.
| Name | Symbol | Conversion |
|---|---|---|
| Kilometer | ||
| Meter | Base Unit | |
| Centimeter | ||
| Millimeter |
Important: Symbols in the metric system follow a consistent set of prefix rules, which we explain below. If you find these difficult, do not worry! For now, you just need to remember the conversions shown in the table above.
The prefix rules are as follows:
The prefix "" stands for kilo, which means . Therefore,
The prefix "" stands for centi, which means . Therefore,
Notice that if we add to itself times, we get exactly Therefore, equals as stated in the table.
- The prefix "" stands for milli, which means . Therefore, This means that equals as shown in the table.
A window is wide. What is this length in centimeters?
A table showing the metric units of length is given below.
| Name | Symbol | Conversion |
|---|---|---|
| Kilometer | ||
| Meter | Base Unit | |
| Centimeter | ||
| Millimeter |
So, is equivalent to
A road is $1\,\textrm{km}$ long. What is this length in meters?
|
a
|
$0.01\,\textrm{m}$ |
|
b
|
$100\,\textrm{m}$ |
|
c
|
$1\,000\,\textrm{m}$ |
|
d
|
$0.1\,\textrm{m}$ |
|
e
|
$10\,\textrm{m}$ |
A shelf is $1 \, \rm{m}$ wide. What is this width in millimeters?
|
a
|
$10 \, \textrm{mm}$ |
|
b
|
$0.01 \, \textrm{mm}$ |
|
c
|
$0.1 \, \textrm{mm}$ |
|
d
|
$1\,000 \, \textrm{mm}$ |
|
e
|
$100 \, \textrm{mm}$ |
Another way to measure length is to use customary units. The most common customary units for length are inch, foot, yard, and mile.
A table showing some of the most common customary units of length is shown below.
| Name | Symbol | Conversion |
|---|---|---|
| Mile | ||
| Yard | ||
| Foot | ||
| Inch |
Let's give some examples of each unit, going from the largest unit to the smallest :
Four loops around a standard running track is approximately
The length of one large stride is approximately
The length of an adult's foot is approximately
The length of an adult's thumb tip is around
Customary units are not standard in the scientific community. However, they are commonly used in the United States and other countries.
Suppose we want to measure the length of a smartphone screen. Which of the following customary units could we use?
A table showing the customary units of length is given below.
| Name | Symbol |
|---|---|
| Mile | |
| Yard | |
| Foot | |
| Inch |
Therefore, from the given options, the only unit of length is
Suppose we want to measure the length of a key. Which customary unit could we use?
|
a
|
$\textrm{oz}$ |
|
b
|
$\textrm{gal}$ |
|
c
|
$\textrm{lb}$ |
|
d
|
$\textrm{s}$ |
|
e
|
$\textrm{in}$ |
Suppose we want to measure the width of a soccer field. Which customary unit could we use?
|
a
|
$\textrm{s}$ |
|
b
|
$\textrm{ms}$ |
|
c
|
$\textrm{yd}$ |
|
d
|
$\textrm{oz}$ |
|
e
|
$\textrm{lb}$ |
The length of a certain canal in Venice is What is its length in yards?
A table showing the customary units of length is given below.
| Name | Symbol | Conversion |
|---|---|---|
| Mile | ||
| Yard | ||
| Foot | ||
| Inch |
So, is equivalent to
Mikayla is approximately $1\,\textrm{yd}$ tall. What is this length in feet?
|
a
|
$2\,\textrm{ft}$ |
|
b
|
$5\,\textrm{ft}$ |
|
c
|
$10\,\textrm{ft}$ |
|
d
|
$3\,\textrm{ft}$ |
|
e
|
$12\,\textrm{ft}$ |
The width of a table is $1\,\textrm{ft}.$ What is this length in inches?
|
a
|
$3\,\textrm{in}$ |
|
b
|
$36\,\textrm{in}$ |
|
c
|
$10\,\textrm{in}$ |
|
d
|
$12\,\textrm{in}$ |
|
e
|
$4\,\textrm{in}$ |