If you are not familiar with U12 shrimp, it's a size of shrimp, meaning that in 1 pound will be under 12 shrimps. It's very large and juicy shrimp. What's the biggest shrimp size? Extra colossal shrimp is the largest size available in seafood markets with counts as large as 5 shrimp per pound. However, there are Asian tiger shrimp that weigh 7-11 ounces each with a count of just 1-2 per pound. I have made with smaller (size 16-20) shrimp, works just perfect.