Rice University's Connexions has a large collection of free learning materials for math students. The searchable Connexions database includes lessons on the metric system, such as Wade Ellis and Denny Burzynski's "Measurement and Geometry: The Metric System of Measurement."
The National Institute of Standards and Technology maintains a capsule history of the metric system and its reception in the United States.
If you do not have a conversion chart or a metric conversion function on your calculator, you can find online converters like the one provided by the University of Houston's math department. This browser-based metric unit converter is cross-platform, completely free and doesn't require you to install any additional software.