### Let’s Think About It

Maya and her family live in Australia. At school Maya is learning about water conservation. She takes a survey online about how her family uses water at home. It asks her questions about how long their showers are, how often they do laundry or run the dishwasher, and whether they water their lawn. Then, the program estimates how much water her family uses in a year. How can Maya determine what metric unit would be most appropriate for this estimate?

In this concept, you will learn how to choose appropriate tools and units for given metric measurement situations.

### Guidance

The **metric system** is the system of measurement primarily used in science and in countries outside of the United States. The metric system includes units of length (meters), mass (grams), and capacity (liters).

When you want to measure something, the first thing you need to decide is what unit of measurement you want to use. You want to use the unit that most closely matches the object you are measuring. You wouldn't want to measure the volume of a swimming pool in milliliters - the number would be too big!

Here are some real world measurement benchmarks to help you to decide the best unit of measurement.

Length:

- A grain of sand is about 1 millimeter long
- A paperclip is about 1 centimeter wide
- A table could be about 1 meter tall
- A road could be about 1 kilometer long

Mass:

- A speck of dust could weigh about 1 milligram
- A paperclip weighs about 1 gram
- A kitten could weigh about 1 kilogram

Volume:

- An eyedropper holds about 1 milliliter
- A juice box holds about 25 centiliters
- A soda bottle holds about 1 liter
- A kid’s pool could hold about 1 kiloliter

Here is an example.

Choose the appropriate metric unit to measure the weight of a pencil.

First, notice that you are looking for a weight. A pencil weighs more than a paperclip but less than a kitten. This means it would be best measured in grams.

The answer is the weight of a pencil would be best measured in grams.

Once you have determined the appropriate unit of measurement, you can select an appropriate tool for measuring.

When measuring the length a small item, it is best to use a metric ruler. You can use metric rulers to measure in millimeters, centimeters, and meters.

When measuring the weight or mass of a small object, you can use a scale or a balance. You can use a scale to measure milligrams, centigrams, grams, and small numbers of kilograms.

When measuring small amounts of capacity, you can use a graduated cylinder. Graduated cylinders can measure milliliters and centiliters.

Here is an example.

Choose the appropriate tool for measuring the weight of a golf ball.

First, notice that you are looking for the weight of a small object. This means you should use a balance or a scale to do the measurement.

The answer is the weight of a golf ball could be measured with a scale.

Here is another example.

Choose the appropriate tool for measuring the volume of water in a chemical solution.

First, notice that you are looking for a volume which is the same as capacity. There is likely a small amount of water in a chemical solution so you can use a graduated cylinder to do the measurement.

The answer is the amount of water in a chemical solution could be measured with a graduated cylinder.

### Guided Practice

Choose the appropriate metric unit for the following measurements.

- The volume of a jug of milk.
- The distance between your house and your school.

For part a, first notice that you are looking for a volume which is a capacity. A jug of milk holds about the same amount of liquid as a bottle of soda. This means its volume would be best measured in liters.

The answer to part a is the volume of a jug of milk would be best measured in liters.

For part b, first notice that you are looking for a distance which is a length. The distance between your house and your school likely contains at least one road and is definitely longer than a table. This means it would be best measured in kilometers.

The answer to part b is the distance between your house and your school would be best measured in kilometers.

### Examples

#### Example 1

What is the best tool to measure a bag of flour?

First, notice that you are looking for a weight. A typical bag of flour is something that you can carry, so it is not too big. This means you should use a balance or a scale to do the measurement.

The answer is the weight of a bag of flour could be measured with a scale.

#### Example 2

What is the best tool to measure the length of a table?

First, notice that you are looking for a length. A typical table is no more than a few meters long. This means you should use a meter stick to do the measurement.

The answer is the length of a table could be measured with a meter stick.

#### Example 3

What is the best tool to measure the amount of water in a glass?

First, notice that you are looking for a volume which is the same as capacity. You can use a graduated cylinder to do the measurement.

The answer is the amount of water in a glass could be measured with a graduated cylinder.

### Follow Up

Remember Maya and her family in Australia? Maya took a survey about her family's water usage in order to estimate how much water her family uses in a year. Maya wonders what metric unit would be most appropriate for this estimate.

First Maya should notice that she will be using a metric unit of capacity. The amount of water a family uses in a year is a large amount of water - more than the amount of water in a pool! This means kiloliters would be the best unit of measurement.

The answer is that the family's water usage for the year would be best measured in kiloliters.

### Explore More

Choose the appropriate tool for the following measurements.

1. The volume of a water balloon

2. The length of a basketball court

3. The weight of an apple

4. The volume of a milk carton

Choose the appropriate unit for the following measurements:

5. The distance between two towns

6. The weight of a peanut

7. The length of a hand

8. The volume of a raindrop

9. The weight of a person

10. The weight of a bag of sand

11. The height of a table

Solve each problem.

12. The town square has a length of 39.2 meters and a width of 17.5 meters. What is the perimeter of the square? [Remember:

]13. A pharmacist mixing cough syrup mixes 1,550 milliliters of syrup, 725 milliliters of cherry flavor and 1.25 liters of water. Once mixed, what is the total volume of the cough syrup in liters?

14. A stable houses horses with the following weights. Arnaud: 331.6 kg; Josie: 331,061 g; Max: 331,612 g; Taboo: 331.61 kg. Order the horses from greatest to least weight.

15. At the farmer’s market, Josh bought 1.5 kilograms of oranges, 150 grams of grapes, and 15,000 centigrams of apples. How many grams of fruit did he buy in all?