Cups deal with volume, while pounds measure weight, so these units cannot be directly converted to each other. However, it is possible to convert cups of water, for example, to pounds. One 8-ounce cup of water weighs about half a pound.
To further complicate matters, there are multiple definitions of "cup." Traditionally, a cup is defined as one-sixteenth of a gallon, which is approximately 236.6 milliliters. However, United States standards define a cup as 240 milliliters for nutrition labeling. Although its use has diminished over the years, the metric cup is defined as 250 milliliters. When converting between volume and weight, temperature and pressure often play a role as well; substances typically take up more space of they are warmer.