The difference between large and jumbo shrimp depends entirely on where you buy them. The terms describing the size of shrimp like "small", "medium", "large" and "jumbo" are not regulated, and vary from store to store. The way to truly know the size of shrimp you are buying is by the number–called "count"–with which they are labeled.
The count gives you the number of shrimp you can expect to get in one pound. The fewer shrimp per pound, the larger and more expensive they are.
Some of the standard sizes you'll find are:
61-70, 51-60 Really small shrimp, often used for shrimp salad. Often labeled Tiny, Extra Small and Small
43-50, 36-42 Labeled medium or medium large. I'd use these in pasta or mixed seafood dishes
31-35, 26-30 These are readily available, often labeled large, and my go-to size when budget is a consideration
21-25, 16-20 Often labeled jumbo, these are my choice when shrimp, prepared with few other ingredients, are the main course. When serving grilled shrimp or simple sautéed shrimp for dinner, each diner might get 4-6 of these.
10-15, usually 10 These are a treat; an indulgence as expensive as they are impressive looking. They may be referred to as colossal.
For recipes using shrimp of various sizes, see our collection of Shrimp Recipes.
Recipe: Spicy Grilled Jumbo Shrimp