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: Liquid Measurement Conversion
Provides tables showing how to convert liquid measurements used for cooking between different customary units and metric units. Covers teaspoons up to gallons, as well as conversions to milliliters.
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