Liquid capacity filled to the brim (no foam)
16 Gallon 1/2 Barrel 1984 oz, 8 Gallon 1/4 Barrel 992 oz, 5.75 Gallon 1/6 Barrel 661 oz

Glassware
The number of servings you can draw from a keg depends on three factors:  (1) Style of Glassware (2) Size of Glass (3) Size of Foam Head.  Some styles of glassware can yield more glasses per 1/2 barrel than others, even though they may have the same volume capacity.  Glasses that are wider at the rim than at the base will yield more because the foam head takes up more volume.  The chart below will give you the estimated servings per 1/2 barrel for the various styles, sizes and desired foam head.