measures of volume

     Measures of volume confuse a lot of people, but it just takes a bit of practice or experience. Our measures were supposed to have been all metric by 1980, they told us in the 1970's, but even that won't help with older books, movies, or recipes. For example--
We still sell gasoline by the gallon. A gallon is equal to 4 quarts ( quarters of a gallon ). A quart is not exactly equal to a, liter, but it's roughly the same.
Alcoholic beverages were traditionally sold by the "fifth", or fifth of a gallon. A "fifth" of a gallon might be labelled four-fifths of a quart--the same thing. So there were five "bottles" of alcohol to the gallon.
Milk is also still sold by the gallon, by the half-gallon, the quart, the pint, or the cup. Each of these is half of the next larger--2 cups make a pint
                         2 pints make a quart
                         2 quarts make a half-gallon
                         2 half-gallons make a gallon.
Cups were divided into ounces, 8 to the cup, or 128 to the gallon.
Liquids sold in liter-sized bottles are an attempt to approximate these familiar measures, so we have 3/4 of a liter, or 750 milliliters ( the same thing ), and so on. The metric system uses tenths, so a liter can be divided into centiliters ( cl's--100ths ) or milliliters ( ml's--1,000ths ).