How do you know how big the shrimp will be?
Shrimp are sold based on their size. The sizes are designated by determining how many shrimp you should expect to find in a pound. For example: 21/25 = you will have 21 to 25 shrimp in a pound.

When you have been cooking shrimp for a while you start to realize what size shrimp are most appropriate for various dishes.
I enjoy using 21/25's most often for my family dishes because I can cut them into thirds and sauté with veggies for a perfect and pretty consistent shrimp meal every time. My kids are still young and if I used whole shrimp, I would be expected to help cut them into bites when I plate them. After cooking a meal, I don’t want to spend a bunch of time cutting the food up for my kids. I prefer to do it all at once.

When I am entertaining or making a dish for an ALL ADULT meal I use 26/30 or 31/35 so I can have plenty of whole shrimp (makes a better presentation) in whatever dish I am preparing.

The smaller shrimp such as the 51/55 are great for various appetizers , to cook into nice red gravy to top spaghetti squash, on top salads or fry into popcorn shrimp. I do not however enjoy peeling these smaller shrimp which is why I'd rather cut the bigger shrimp into 3rds when “presentation” isn’t as important as the nourishment and flavor.

16/20's are the perfect date night shrimp or to pair 4-5 of them with a small bit of steak for a perfect surf-n-turf for an ALL ADULT meal. When they get much bigger I like to boil them and puree into fantastic shrimp bisque. Hope this helps.