There is no set amount of coffee that needs to be put in a 12 cup Mr Coffee. However, it is generally recommended that around 2 tablespoons of coffee grounds are used for every 6 ounces of water. This means that if you are using a 12 cup Mr Coffee, you would need around 24 tablespoons of coffee grounds. It is important to note, however, that everyone's taste for coffee varies, so feel free to adjust the amount of coffee you use to your liking.