ASK DR. BOLI.

Dear Dr. Boli: I bought a can of German beer, and on the label it says, “500 ml, 0.5 l, 50 cl.” So my question is this: How many deciliters is that? Math is hard. —Sincerely, Just Wondering.

Dear Sir or Madam: 4.71. One of the curious facts about beer as a physical substance is the property known to science as the non-conservation of deciliters. Because this property frequently confuses consumers and causes them to believe they are drinking less beer than is actually in the can, the Reinheitsgebot in Germany specifies that beer must be labeled in milliliters, liters, and centiliters, but not deciliters.