Meters, liters, and grams

Do you have any suggestions for how I can help my middle school students understand and use the metric system? We struggle with this at the beginning of every year.  –E., Indiana

It’s hard for U.S. students to get a handle on meters, liters, and grams when in their everyday lives they are surrounded by references to miles, feet, inches, quarts, and pounds (one exception being a two-liter bottle of soda). We can’t change what’s on television or on the internet, but we can require that students use International System (SI) units and measurements in their science activities, investigations, and reports.

The first textbook I used had a chapter devoted to the metric system, so I would dutifully “cover” it at the beginning of the year, supposedly to prepare students for future investigations. The students memorized the prefixes, and there were exercises in measuring classroom objects. The chapter had a heavy emphasis on converting units from metric to English or vice versa. What a disaster! I felt like I was teaching more arithmetic than science. Even though we practiced measuring things with metric rulers, graduated cylinders, and balances, I found that later when it came time to actually apply those skills in investigations, my students had forgotten (or claimed to have forgotten) much of what they “learned.”

When I reflected on this, I realized that I had expected the students to master these concepts, skills, and vocabulary without a meaningful context for them. It seemed difficult for them to apply processes introduced at the beginning of the year to an activity weeks later. I was certainly teaching the material (with the lesson plans to prove it), and the students seemed to know the material at the time. But they weren’t learning it well enough to apply it to new activities without a lot of review and re-teaching.

So in the following years I changed my approach. I decided to introduce only those SI/metric measures that are commonly used: kilograms, grams, and milligrams; liters and milliliters; kilometers, meters, centimeters, and millimeters. That’s it. I mentioned that other units such as decigrams or centiliters exist but are seldom used. (I’ve traveled a lot in Europe, Canada, and Australia and I never saw anything measured in hectograms or kiloliters!)

I introduced or reinforced these units within the context of investigations, rather than as separate and isolated topics of instruction. When we came to an investigation requiring liquid measurements, we first practiced with graduated cylinders and discussed the relationship between milliliters and liters. Students had a section in their notebooks for notes and drawings on measurements that they could use as reminders in future activities. I also found that students knew more than I had assumed.

We didn’t spend time on problems converting miles to kilometers or grams to ounces. It’s not worth it, and now most smart phones, tablets, and computers have apps that do these conversions. Students should know which SI units correspond to the ones they are more familiar with in the United States. For example, in much of the world meat and butter are sold in kilograms instead of pounds, distances between places in kilometers, gasoline and milk in liters, and so on.

I always had a few students say “Why do we have to measure this way?” which is a good question. I would mention that science research around the world uses SI measurements. The United States, Myanmar, and Liberia are the only nations in the world that do not use SI as the official system of weights and measures. But I clinched the discussion by asking students, “Who likes to play with fractions?” Very few hands were raised. When the students compared adding 1/8 inch and 3/16 inch vs. adding 3 mm and 4 mm they were convinced.

See the websites:

Meaningful Metrics with Dramatic Demonstrations

Metric Units


Photo: NASA 

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5 Responses to Meters, liters, and grams

  1. Nicole says:

    Why don’t use change everything around them while you have them. Make a store and change their whole world, give extra credit to those who try it at home..

  2. Mary Bigelow says:

    I received the following communication from the NIST Metric Program:
    Your readers may be interested to know that K-12 educators may request a free SI Teacher Kit from the NIST Metric Program ( Each teacher may directly contact the office at and include their name, school, subject, grade level, phone number, and mailing address. The NIST SI Teacher Kit contains a classroom set of metric rulers (NIST SP 376 – a 300 mm ruler), laminated metric conversion cards (NIST SP 365), SI Education CD, and other measurement resources.
    Our website has numerous educational materials that can be downloaded and freely reproduced. These resources are helpful to students as they become familiar with the metric system (e.g., developing reference points or that innate understanding of how much a quantity is) and learn more about SI basics:
    · Education Resources
    · Everyday Estimation
    · Becoming Familiar with the SI
    · Writing with SI Units
    They may also enjoy a new comic book-style video animation featuring the League of SI Superheroes, which is available on the NIST YouTube Channel ( and was developed to help middle school students learn about the 7 base measurement units. In their first adventure, Desperate Measures, the SI Superheroes use the power of measurement to help a stranded soccer player get home! In their second episode, Running Out of Time, the League battles archvillain Major Uncertainty in a race to keep the world’s satellite navigation system “on time” to help a traveler and his son lost in the desert. The cast of characters include: Mole, Professor Second, Monsieur Kilogram, Mizz Ampere, Dr. Kelvin, Meter Man, and Candela.
    NIST is also currently conducting the Minecraft Video Challenge ( to encourage students to create one or more video clips in Minecraft that teaches others about what the seven base units of the International System of Measurement (SI) are or why they are important in a fun way. Links to the completed videos can be placed in the comments section on the NIST YouTube Channel (
    Best regards,
    Elizabeth J. Gentry
    National Institute of Standards and Technology
    Office of Weights and Measures
    Laws and Metric Program

  3. In addition to the NIST metric system resources, you’ll find a few others related to the metric system on NSTA’s Freebies for Science Teachers web page ( and in the similarly titled column in NSTA Reports (

  4. Sean Ballard says:

    Hi Mary- I teach 8th grade physical science in a small Northern California school district and your description of your personal journey through teaching the metric system really resonates with me! First off, every year I have at least one student who asks me if they should use the “little inches or the big inches” on their meter sticks! (This usually comes after days of instruction and practice on metric units and conversions.) I think this really highlights your comment about student confusion over unit systems. Second, I have learned to be cautious about downplaying certain units of measurement. For example, two years ago I told students that I had never encountered a use for decimeters. A student raised his hand, begging to differ, who informed me that rates of CO2 and water transpiration from leaves are measured in grams per square decimeter per hour. I stood corrected! Lastly, regarding unit conversions, while I agree that at the K-8 level teaching conversions between metric / conventional units is confusing for students, dimensional analysis, as taught at the high school chemistry level, is a really useful engineering skill. For example, in my prior career as a semiconductor (chip) engineer I became familiar with one piece of equipment that had up to twelve units for measuring pressure (militorr, bar, ATM, mm of mercury, psi, kPa, etc.) This was because it used gauges provided by various international suppliers. Wending my way through the thicket of units required more than single-factor conversions, and my training with dimensional analysis was key! Thanks for your great article!

  5. Susan Rollinson says:

    I’m catching up on periodicals after spending some time in India and came across your article on teaching the metric system. India is mostly on the metric system, but residential units are measured in sq ft, and land is in acres. Everything else is metric (m, km, L, g, kg, etc.) Go figure! (Literally!)
    Also, I saw KL a lot in India. Water tanks were labeled “20,000 KL”, etc. Tanker trucks on the road were also given KL capacities. On the other hand, our own roof-top water tank’s volume was given as 5 cubic meters.
    Most of the time I just use metric units in class — compare them to the more familiar English units, but just tell students that if you need metric units, get a metric measuring device. But once I taught chemistry as part of manufacturing certificate program. Because the US is on English unit, but most international sales are in metric units, we had to cover conversions. More reason for the US to convert to the metric system!
    If you want to read an interesting book on how the English system became entrenched in the US, even though early thinkers, such as Thomas Jefferson, preferred the metric system, dig up a copy of the book “Measuring America” by Andro Linklater (2002).

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