How Big is it?

Author: Brink Harrison

Time: one class period
Preparation Time: 5-10 min copying overheads
Materials: US System overhead
Metric system overhead
Metric prefixes

Students will review the units of the metric system, convert from the US system of units of measure to the metric system, and estimate measures before converting between the two systems of measurement.

Purpose – The students will become more familiar with the units of the metric system and use unit analysis to convert from US units to metric units or metric units to English units.


Students will be able to:-

i. Convert from US units of measure to metric units of measure using unit analysis
ii. Convert from metric units of measure to US units of measure using unit analysis
iii. Determine whether their converted measurement is reasonable

National Science Education Standards
Understand measurable attributes of objects and the units, systems, and processes of measurement
Apply appropriate techniques, tools, and formulas to determine measurements

Teacher Background
If applicable

Related and Resource Websites





Ask the students, “If a pen pal of yours, who lives in Germany, writes that she is 182 cm tall, would you know if she’s taller or shorter than you are? How would you tell her your height if all she knows is the metric system?”

Tell the students, “Most of you have grown up using the US/Imperial units for measuring distance, weight, and volume. But most other countries use the metric system. Science teachers require that you know and use the metric system. Why do you think this happens?” Allow time for discussion of how the systems are different and why the metric system is more uniform.

Put up the US System of Measures Overhead, found at the following web site http://www.ex.ac.uk/cimt/dictunit/dictunit.htm#US to show the students just how complicated our system is with the varied numbers you need to remember to change from one unit to another.

Put up the Metric System of Measures Overhead found at the following web site http://www.ex.ac.uk/cimt/dictunit/dictunit.htm#metric to show how the metric system is based on always using 10 to change from one unit to another.

Remind the students that they have probably seen many of the prefixes on the metric units of measurement before. Put up the Metric Prefixes overhead found at
http://www.convert-me.com/en/metric_conversions_en.html Tell the students that between “deca” and “deci” is where the regular unit (meter, gram, etc.) would go. Tell the students that they should definitely know the prefixes from “milli” to “kilo” and how to convert from one unit to another. Two good web sites for checking the students’ abilities to convert between the units of the metric system are http://www.coe.uh.edu/archive/science/science_lessons/scienceles3/metric/metric.html#metricch and Metrics PowerPoint presentation by Dr. Register - Rogers State University, Oklahoma. (http://www.drregister.com/resources/sciprof/ppts/)

Ask the students, “How do we convert from US units to metric units or the other way around? What do we need to know and what do we need to do?” Go to either of the following web sites http://www.bartleby.com/61/charts/M0182500.html or
http://hemsidor.torget.se/users/b/bohjohan/convert/conv_e.htm to find the following conversion factors.

1 km 0.62 miles   ( 1 mile 1.61 km )
1 cm 0.39 inches   ( 1 inch 2.54 cm)
1 kg 2.20 lbs   ( 1 lb .45 kg)
1 US gallon 3.78 liters   ( 1 liter 0.26 US gallons)
1 quart 0.95 liters   ( 1 liter 1.05 quarts)

Have the students estimate the following conversions without calculators.

1. 20 miles     _____ km

2. 25 kg       _____ lbs

3. 100 cm    _____ inches

4. 15 gal      _____ liters

Have the students find the exact values by using a method called unit analysis. Do the following problems with the students, making sure that the students state and cancel the units as they do the problems.



The one of the common problems associated with traveling outside of the USA is being able to estimate how the measurements compare to what we use. This site is an excellent one to help you understand those road signs and store quantities when traveling in Europe or anywhere else that uses metric.
1. A road sign shows 150 km to Paris. How far would that be on your car's odometer?
2. The speed limit is 120 km per hour. How fast should you be going?
3. Your hostel is at an altitude of 1100 meters. How many feet above sea level is it?
4. You can take 25 kg on the airplane as carry on. How many pounds can you take?
5. Would 50 g of bologna be enough for two sandwiches?
6. Your car takes 40 liters to fill the tank. How many gallons is this?


7. A friend asks how many km it is from Los Angeles to San Francisco, a distance of 385 miles.
8. You have a 3000-gallon swimming pool. How many liters would it take to fill the pool?
9. My cat is 35 lbs. How many kg is this?
10. Convert your height from feet and inches to centimeters.

Embedded Assessment

Informal discussion as the students look at the various overheads will allow you to assess their understanding of the US and metric systems of measurement. Informal observation when the students are estimating conversions allows assessment on their understanding of the conversion factors between the two systems. Guided practice and informal observations can be used to assess the students’ abilities to perform unit analysis.


























PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

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Last update: March 7, 2007
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