Convert-me.com - Converts most types of measurements.

Online Conversion - Calculates measurement conversions and many other types of conversions.

Dictionary of Units - This provides a summary of most of the units of measurement to be found in use around the world today.

English Weights & Measures - Imperial weights and measures, English weights and measures, Customary weights and measures - they are all the same (almost!).

NIST Office of Weights & Measures - The Office of Weights and Measures (OWM), one of the longest running and best known programs of the National Institute of Standards and Technology (NIST), promotes uniformity in U.S. weights and measures laws, regulations, and standards to achieve equity between buyers and sellers in the marketplace.

RefDesk - Weights & Measures Resources.