Formerly a keg was a small barrel made by a cooper used to transport items such as nails. Today keg connotes a metal container used to hold beer and other alcoholic drinks under high pressure.

A keg is a standard unit of measure. A full Keg is actually a 31 gallon barrel, but due to the unavailability of full kegs a half-keg is what most people commonly consider a keg. A keg in most contexts has a volume of 15.5 gallons.

1 keg =

     = 56.78 liters
     = 15.5 gallons
     = 75 fifths
     = 1,920 fl oz (US)
     = 1,097 shots
     = 160 drinks (12 oz)
     = 1,280 jiggers
     = 3,840 Tbsp (US)
     = 11,520 tsp (US)
     = 12.50 Gal (UK)
     = 240 cup
     = 1998.42 fl oz (UK)
     = 56781.18 mL
     = 120 pints
     = 60 quarts
     = 3465 in3
     = 2.005 ft3
     = 0.074267 yard3
     = 0.34695 barrels(British)
     = 0.35714 barrels (US Oil)
     = 24.0625 board feet
     = 1.5613 Bushels (British)
     = 1.6113 Bushels (US)
     = 15,987.37 drams (Brit, flu)
     = 15360.00  drams (US, flu)
     = 1.3878 firkins (Brit, flu)
     = 12.890625 gal (US, dry)
     = 399.6842 gills (Brit)
     = 959,242.16 minims (Brit)
     = 921,500.0 minims (US)
     = 6.2450 pecks (Brit)
     = 6.4453 pecks (US)
     = 99.9211 pints (Brit)
     = 103.125 pints (US, dry)
     = 49.9605 quarts (Brit)
     = 51.5625 quarts (US, dry)
     = 140309.34 acre Angstrom
     = 7.6722 * 10 - 7 acre fathom
     = 0.0004464 rod3
     = 6.7059 x 10 - 50lightyears3
     = 0.0000057 hectare meter
     = 0.000046 acre feet
     = 1.69601 10 - 35AU3 

Expression of the size of a keg in astronomical units presents a bit of a quandary. In the absence of gravity, CO2 comes out of solution with the liquid beer. However, Dutch scientists have invented a device for "space beer" which releases beer globules consumable with a straw. With this developement coming on the tails of their invention of a vacuum-powered space-pizza table suggests a dramatic increase in the quality of life among astronauts.

A keg, as in beer keg comes in multiple sizes.

 Size            12 oz drinks      16 oz drinks
 -------------------------------------------------
 5.0 Gallon      53                40
 7.75 Gallon     82                62
 13.2 Gallon     140               105
 15.5 Gallon     164               124

Tapping a keg

Tapping a keg should be done carefully and reverently. As long as you pay attention to what you are doing its a straightforward operation of just a few steps:

• Remove the keg cap
• Line up the notch on the tap with the notch on the keg
• Insert the tap into place and twist clockwise to lock it there
• Push the leaver all the way down, which will open the keg

Note: There is no need to pump the keg when it is first opened, the pressure inside the newly tapped keg is plenty to get the beer flowing.

According to the warning on the keg cap from Anheuser-Busch, Inc., a keg can cause injury of it is overpressurized with compressed air or with C0₂.

"The tapping system and pressure regulator both should be equipped with a pressure relief (blow off) device. If you are not familiar with tapping equipment, consult your retailer..." -- Anheuser-Busch's Keg Cap

See also barrel, firkin, kegger .

References

• Brooks, Michael. "Space Bar". New Scientist, 22 Dec. 2000