How many ounces of boneless chicken breasts should I buy for a recipe that calls for 3 cups of cut up chicken breast?

I have a recipe that calls for 3 cups of cut up chicken breast. How many ounces of boneless chicken breasts should I buy? I find I frequently have trouble with recipes, which call for one measure, but the grocery store sells in another measure. Could you post some equivalents?
About 18 ounces or 1.125 pounds (about 4.5 raw boneless, skinless chicken breasts weighing 4 ounces each) would yield 3 cups of raw chicken breast. I have seen some rather large chicken breasts in my local grocery stores so go by weight rather than counting the number of breasts as long as the chicken is going to be cut up. The number of servings in the recipe would give you a clue as to the number of chicken breasts to buy unless it is a casserole or stir fry that extends the meat required. Generally, a chicken breast weighing 4 ounces raw (boneless and skinless) and measuring about 2/3 cup (per raw breast in cut pieces) is the same as 3 ounces of a cooked chicken breast.