The general rule is at bottling time, mix 5 ounces by weight, of dextrose (corn sugar) in 2 cups of filtered water and bring it to a boil. Cool it to around 70F and mix it in. This simple process premixes the required sugars in the beer, so that when bottled, it will be nice and fizzy in a couple weeks... This gives a good general amount of fizz to the beer.