National Council of Teachers of Mathematics
The Math Forum: A Tour of Measurement
Peruse a collection of lesson plans, resources and FAQ's about measurement at every grade level.
Wolfram Research
Wolfram Science World: United States System of Liquid and Dry Measures
Unlike the British Imperial system, the United states uses two different systems, one for liquid volumes and one for dry volumes. Confusingly, these two systems share the units of quart and pint, which have different values. This site...