When purchasing shrimp, you may have noticed a set of numbers on the packaging or seafood case label, such as "21/25" or "51/60". This number is called the "count" and it informs consumers of the size of the shrimp. The number actually refers to how many individual shrimp it takes to make a pound. For example, when buying a pound of "21/25" count shrimp, you can expect to receive 21-25 individual shrimp for that pound.
The smaller the number, the larger the shrimp. Occasionally you will find a count that shows the letter "U," such as "U/10." This means that there are "under" the number in the count of the shrimp; "U/10" explains that you will find "under 10" shrimp per pound.
By using the count for purchasing shrimp, you can guarantee that you have a consistent measure of the product. This is a much more reliable way to get a good measure of shrimp per pound that going by labels such as "jumbo" or "large," as those labels are not standardized; what's labeled "small" in one store might be "medium" in another.
Picking the right count shrimp for your recipe is often a matter of personal choice, but there are a few guidelines. When creating a shrimp salad or adding shrimp to a green salad as an accent, you might choose the tiny 250-350 count shrimp. For grilling, reach for the larger 16-20 count. A general rule of thumb for purchasing shrimp is 1/4 pound raw shrimp per person.