As mentioned above, the total capacity of a car trash bag varies dramatically from model to model. While some list the capacity in liters, not all do, and figuring out just how much any given model will hold can be tricky. Looking at the dimensions and comparing them to the size of a soda can will give you an idea of how much a particular trash bag can hold. Check online user reviews too. If you're still unsure, it might be a good idea to size up just in case.