USDA guidelines count 1 cup (8 fluid ounces) as a serving. There are 16 cups in a gallon. Countries other than the US may have different official guidelines.
A portion is different from a serving and is usually defined as what would be a reasonable amount to consume at one meal. A child may drink a single serving at a meal but a teenager or adult may consume 2 servings in order to consume enough nutrients for the day. It's important to consider how much your family typically consumes if you're planning meals or making a grocery list.
16 1 cup servings.
1 gallon = 16 cups
1 cup =0.23 gallon
16
That is 20 servings
A half gallon has 64 fluid ounces total, so to divide it into 4-ounce servings, you would divide 64/4. So there are 16 servings
16
1/2 gallon = (64 fl oz) / (4 fl oz per serving) = 16 servings
It would have to be under 16. Eight ounces is considered a serving of water, and there are 128 ounces in a gallon. That divides out to 16 servings. Now, milk has fat, protein, and vitamins in it, not just water, so you would have to get at least a little less water than 16 servings.
16 8-ounce servings per gallon. (1 gallon is 128 fl oz.)
4 servings
64 fl oz / 4 fl oz = 16 servings
16
16
64