The Maß (pronounced ) or Mass (pronounced ) is the Bavarian language word describing the amount of beer in a regulation mug, in modern times exactly 1 litre (33.8 US fl oz).
Maß is often used as an abbreviation for the handled drinking vessel containing it, a Maßkrug. Ubiquitous in Bavarian beer gardens and beer halls and a staple of Oktoberfest it is often acceptably referred to as a beer mug by English speakers but may only be a beer stein if made of stoneware and capable of holding a regulation Maß of beer.
The word "Maß" can be of either neuter or female grammatical gender. In its neuter form, das Maß, it is the German word for "measure". Its feminine version, "die Maß", is used in southern Germany and Austria to refer to a one-litre glass beer mug or its contents. It is spelt "Maß" or "Mass" (both spellings are allowed) in Germany and Austria, "Mass" in Switzerland. The plural is Maßkrüge.
In the Southern German areas (Austro-Bavarian), the Maß originally measured 1.069 litres, equivalent to 2.259 US or 1.881 UK pints. Other German speaking areas had different measures: in Switzerland between 1838 and 1877 and in Baden until 1871 the Maß was 1.5 litres.
The modern Maßkrug is slightly larger than 1 litre, with a (calibration mark) denoting the level to which the beer must be filled to allow room for its head to expand. Using mugs without a calibration mark, or with a mark that is below the true 1 litre position, is also prosecuted as fraud. A "Coalition against fraudulent pouring [of beer]" ("Verein gegen betrügerisches Einschenken") in Munich fights for the customer rights of beer drinkers, and is mostly active on the Oktoberfest.
Since beer for immediate consumption is usually sold in smaller amounts, between 0.2–0.5 litres (6.8–17 US fl oz), in the more northerly parts of Germany, the Maß has mostly fallen out of use there, except for Bavarian-themed events.
Mugs are frequently decorated with a print of the sign of the brewery.
Some beer gardens and restaurants rent space out to patrons to store their mugs, which often have personalized engravings on their lids. For a small monthly fee the establishment will also wash one's mug.