The average beer Keg holds around 15.5 gallons of beer which is quite a lot of beer especially for one person and out of that 15.5 gallons of beer in the beer keg you would get 165 12 ounce beers from a beer keg.
Or if you had 16 ounce beer mugs you could get 124 of those 16 ounces of beer from one beer keg.
One beer keg can serve quite a bit of people and if it's only you drinking the beer it will last awhile unless you're an alcoholic.
You can easily get pretty drunk when drinking a keg of beer all by yourself.