Shrimp are sold by count per pound.
Counts are expressed as a range. For example, 26/30 means the shrimp are of such a size that 26 to 30 of them make up one pound. The smaller the size, the higher the counts.
Counts are occasionally expressed in names rather than numbers, such as "colossal," "jumbo," and "extra large." Since these appellations are not universally defined and regulated, the numbers system works best, especially since one man's "jumbo" is another man's "medium".
The following rules usually apply when referring to the size of headless, raw shrimp...
H O W S H R I M P
A R E S O L D
Most shrimp caught on the East Coast fall into the 16/20 – 36/40 range.
We occasionally catch larger or smaller shrimp, but you can generally count onshrimp that are considered medium – large
H O W M U C H S H R I M P T O B U Y
The important question about shrimp for most of us is,
"How much do I need to buy for "x" number of people?"
Allow about 3/4 pound of tails (headless shrimp in the shell) per person; if the shrimp are shelled, figure about 1/3 to 1/2 pound per person.
Other useful information:
A good rule of thumb is that 2 pounds of shrimp in their shells will yield about 1 1/4 pounds when peeled.
One pound of shrimp with their heads on yields just over .6 pounds of tails (heads-off).