When trying to figure out how to measure 5oz or 6oz or any odd measurement like that for my orange juice, I noticed that my son's cups from restaurants tend to have ounces measured on the side. This is a quick way to measure my morning juice or tea without pulling out measuring cups.
I found the cups mainly at red robin. My mother loves to go there with my son and he gets to bring the cup home. Each ounce line is marked with a cute little saying and is a big help in getting just the right amount.