Remember Jose and the picnic tables and place mats in the Appropriate Tools for Metric Measurement Concept? Well, now that Jose has figured out which tool to use, he needs to decide on the measurements for his place mats.

Jose knows that he is going to use a ruler, but isn't sure if he will be measuring in millimeters or centimeters.

What do you think?

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This Concept will explain how to best choose decimal units for given measurement situations. You will learn how to help Jose with this question.
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### Guidance

Now that we know about using the appropriate tool, we also need to choose the best unit to measure different things. The common metric units of length are
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millimeter, centimeter, meter and kilometer.
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When is the best time to use each measurement?
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You can think about this logically. Let’s start with millimeters.

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A millimeter is the smallest unit. There are 10 mm in one centimeter, if an object is smaller than one centimeter, then you would use millimeters.
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Who would use millimeters?
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A scientist measuring something under a magnifying glass might use millimeters to represent a tiny specimen.

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A centimeter is the next smallest unit. We can use a ruler to measure things in centimeters. If an object is the length of a ruler or smaller, then it makes sense to use centimeters to measure.
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Meters are used to measure everything between the length of a ruler and the distance between things in a room.
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Most household objects such as a tables, rooms, window frames, television screens, etc. would be measured in meters.

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Kilometers are used to measure distances. If we are looking to figure out the length of a road, the distance between two locations, etc, we would use kilometers.
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Think about each example and then choose the best unit to measure each.

#### Example A

The height of a picture on the wall

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Solution: Meters
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#### Example B

A caterpillar

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Solution: Centimeters
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#### Example C

The width of a penny

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Solution: Millimeters
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Now let's go back to Jose and the place mats. Here is the original problem once again.

Remember Jose and the picnic tables and place mats in the Appropriate Tools for Metric Measurement Concept? Well, now that Jose has figured out which tool to use, he needs to decide on the measurements for his place mats.

Jose knows that he is going to use a ruler, but isn't sure if he will be measuring in millimeters or centimeters.

If Jose is going to use a ruler, there are only two options for measurement. These are either millimeters or centimeters. Jose has chosen two measurements that are accurate.

Now which one should he use?

Well, millimeters is a very tiny measurement unit. If you think about a place mat, it is about the same size as a piece of paper, or a little larger than that. If Jose uses millimeters, it would be very difficult.

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Therefore, it makes sense for Jose to use centimeters to measure his place mats.
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### Vocabulary

- Metric System
- a system of measurement

- Length
- the measurement of a object or distance from one end to the other

- Millimeter
- the smallest common metric unit of measuring length, found on a ruler

- Centimeter
- a small unit of measuring length, found on a ruler

- Meter
- approximately 3 feet, measured using a meter stick

- Kilometer
- a measurement used to measure longer distances, the largest common metric unit of measuring length

### Guided Practice

Here is one for you to try on your own.

Jesse is going to rearrange all of his furniture. He wants to know if his sofa will fit between two windows on the east wall of the room. Which unit would he use to measure the distance between the two windows?

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Answer
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Since Jesse is measuring something larger than a ruler, he would use meters to measure the space between the two windows.

### Video Review

James Sousa, Converting Between Metric Units

Other Videos:

- http://www.mathplayground.com/howto_Metric.html – This video expands on the basic information of the metric system. It also begins working with metric conversions.
- http://www.teachertube.com/viewVideo.php?video_id=8896 – The Metric System song to “Arms Wide Open” by Creed this is sung by two science teachers.

### Practice

Directions: Choose the best metric unit for each measurement situation.

1. A paperclip

2. The width of a dime

3. A tall floor lamp

4. The width of a room

5. A road race from start to finish

6. The wing span of a butterfly

7. The wing span of an eagle

8. A shoe size

9. The width of a window

10. The floor space of a tent

11. The distance from the bottom of a mountain to the top

12. The perimeter of a garden

13. The area of a garden

14. The distance from one city to another

15. The size of a fingernail

16. The length of a small table

17. A book

18. A cell phone

19. The length of a room

20. The distance from Boston to Cincinnati