A water bottle, in this context, means a single serving size. We chose to use a 16.9-ounce bottle for our calculations, as this is the most common option. To calculate how many 16.9-ounce bottles of water are in a gallon, we need to know how many ounces are in a gallon. We use a free online conversion calculator for measuring liquids to determine that there are 128 ounces in a gallon.
Divide 128 by 16.9, round it up and we now know that there are eight bottles of water in a gallon. Let's understand the relationship between ounces and gallons. Now that you know how many ounces are in a gallon according to the American system, let's review the different measurement systems that exist around the world.