Purple Math
Purplemath: Metric Units & Converting Between Them
This resource demonstrates how to convert between various sizes of metric units quickly and easily. Metric units are very nice to work with, since they are all multiples of ten (or a hundred, or one-tenth, etc) of each other. You can...
Science Struck
Science Struck: Metric Measurements: Units and Conversions
Discusses how the metric system of measurement was developed and provides tables of unit conversions within the metric system, within the Imperial system, and between the two systems.
Cool Fire Technology
Customary & Metric Systems of Measurement Area Measure
Scroll down to the bottom of the page to view a table which lists measurement conversions for area.
Other
Conversions for Weight Measurements
This site allows you to convert weight/mass measurements. For example converting tons to grams. CCSS.Math.Content.3.MD.A.2 Measure and estimate liquid volumes and masses of objects using standard units