The most common types of sterile gauze pads are four inch square patches commonly called "four-by-fours." Buy them individually wrapped rather than in bulk for best results.
Heavy duty injuries may require something a little bigger than four inches on a side. Thick five inch by nine inch pads are used in surgery and often referred to as "abdominal pads." Even larger wounds may need "trauma dressings" for complete cover.
Another option is to use roller gauze. Roller gauze can be tied around an arm or leg to control bleeding without using tape to hold the gauze in place.