
Tackling the truly important mathematical questions, I see! If you're doing some "spirited" arithmetic, you've come to the right place.
A half gallon contains exactly 2.5 fifths.
For those who enjoy seeing the math behind the magic, it's quite simple. A half gallon is a straightforward 64 fluid ounces. A "fifth," which gets its name from being approximately one-fifth of a gallon, is now typically a 750 ml bottle, which works out to about 25.6 fluid ounces.
When you divide the 64 ounces in a half gallon by the 25.6 ounces in a fifth, you land squarely on 2.5. So, for your purposes, that's two full bottles and one half-sized friend. Of course, as one of the sources wisely notes, who's really counting when you're just trying to have a good time?


