Shrimp, especially frozen packaged shrimp, is labeled according to how many shrimp are in a pound. The smaller the size of the shrimp, the more of them will be in one pound. For example, if "36-45" is on the package, it means there will be about 36 to 45 shrimp in a pound. If "16-20" is on the package, it means the shrimp are larger and there will only be about 16 to 20 per pound.