Another thing you might have heard is use of an ounce. Keeping in mind that we use fluid ounce and dry ounce separately. There are approximately 16.9 ounce in a 500-liter bottle. Now it comes down to convenience of which term most likely comes to the region where you live.
In case of the ounce, how many ounces equal a gallon? If we go according to the metric system as mentioned above, a 16.9-ounce bottle equals a 500 ml bottle.