**Introduction**

In this lesson, you will review the concept of units, specifically perimeter, area, and volume. Units can tell you what a number means (e.g., 55 kilometers).

This video illustrates the lesson material below. Watching the video is optional.

**What is a Unit?**

Units describe the quantity and value of a number. Units are very important. Without units, you cannot reference what the number represents in a given circumstance. For example, if you go into a store and there is a shirt that has a tag with the number 3. The number 3 has no units and therefore does not provide enough information for you to know the cost of the shirt. The shirt needs to have a unit with the number 3 so customers have enough information to purchase the item or not. Think about these other examples:

- A recipe. With no units, how can you make the food?
- Temperature. There is a big difference between 30 degrees Fahrenheit and 30 degrees Celsius

Figure 1

**Different Types of Units**

There are different kinds of units. Note the examples below.

- Length: m (meter)
- Mass: kg (kilogram)
- Time: s (second)
- Electric Current: A (ampere)
- Temperature: K (kelvin)
- Intensity of Light: cd (candela)
- Amount of Substance: mol (mole)

The metric system uses meters, meters squared (\(m^2\)), and meters cubed (\(m^3\)), as well as millimeters, centimeters, kilometers, and many other units. The metric system also uses grams and kilograms for weight.

Metric Units:

- Kilo- 1000 units
- Hecto- 100 units
- Deka- 10 units
- Deci- 0.1 units
- Centi- 0.01 units
- Milli- 0.001 units

Metric Conversions:

- To convert to a larger unit, move the decimal point to the left or divide.
- To convert to a smaller unit, move the decimal point to the right or multiply.

The United States usually uses units like inches and feet for length, inches and feet squared for area, and inches and feet cubed for volume. There are also yards, miles, and other units to represent longer lengths. Ounces are also used in volumes and weights. Weights can be measured in pounds as well which is abbreviated as ‘lbs.'

U.S. Customary Units:

- Length
- 12 in = 1 ft
- 3 ft = 1 yd
- 5,280 ft = 1 mi
- 1,760 yd = 1 mi

- Weight
- 16 oz = 1 lb
- 2,000 lb = 1 ton

- Capacity
- 16 fl oz = 1 gal
- 2 pt = 1 qt
- 8 pt = 1 gal
- 4 qt = 1 gal

- Time
- 60 sec = 1 min
- 60 min = 1 hr
- 24 hr = 1 day
- 7 days = 1 wk
- 52 wk = 1 yr
- 12 mo = 1 yr
- 365 days = 1 yr

Temperature has three common unit scales: Celsius, Fahrenheit, and Kelvin. Kelvin units are used often in science. Time also has its own sets of units: seconds, minutes, hours, days, years, and even centuries. A candela is a unit used to describe the luminosity of something, and an ampere is used to describe electric current.

These are just a few of the many units that are used in the world on a daily basis.

**Things to Remember**

- Units tell you what the number means.
- There are many different things in the world that you need to know the units for.

### Real World Application

What is a unit you use frequently in your life? You might use it in your work, home, cooking, or measuring. Anything you measure requires a unit.

### Practice Problems

**1. Which of the following units are used to measure temperature?**(

a. Ounces (oz)

b. Degrees Celsius (°C)

c. Kilograms (kg)

d. Inches (in)

**2. Which of the following units are used to measure length?**(

a. Meters (m)

b. Pounds (lbs)

c. Liters (L)

d. Degrees Fahrenheit (°F)

**3. Which of the following units are used to measure area?**(

a. Liter (L)

b. Degrees Celsius (°C)

c. Square feet (\({\text{ft}}^2\))

d. Miles (mi)

**4. Which of the following units are used to measure area?**(

a. Quart (qt)

b. Degrees Celsius (°C)

c. Square centimeters (\({\text{cm}}^2\))

d. Miles (mi)

**5. Which of the following units are used to measure time?**(

a. Minutes (min)

b. Pounds (lbs)

c. Dollars ($)

d. Centimeters (cm)

**6. Which of the following units are used to measure weight?**(

a. Seconds (sec)

b. Kelvin (K)

c. Feet (ft)

d. Pounds (lbs)

**Need More Help?**

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