I was shopping in the grocery store last night and picked up orange juice (now, just for the record, I don't generally look for ounces first, I look for what country the oranges came from - I try to always choose USA).
Now, as I was looking for the 'USA only oranges' label, I noticed the ounces marking beside it. Want to know what it said '59 ounces'. 59 ounces is NOT a half gallon, 64 is.
Do you want to know what is very sad - I bet there are a millions of people who would not know that 59 ounces is not a half-gallon.
Case in point, I had a semi-argument with a stock person one day while trying to find a gallon of regular bleach - she insisted that the 96 ounce bottle was a gallon, I tried to reasonably tell her that no, a gallon is 128 ounces, not 96. She looked at me like I had 3 heads and said something like "Well, these are our gallons." Really? Gallons are different based on store now?
Anyhoo - check your ounces and make sure you figure that into your calculations