I am always asked how much fondant do I need to cover a cake. It all depends on what size your cake is, below I have a guide that will help you in your decision making. Remember that all of these sizes are for a 4-inch high cake. If you are a beginner always start off using a bit more fondant than the guide calls for. It's better to have extra than to not have enough. When you are done covering and decorating your cakes, and you happen to have extra fondant that you won't be using for a bit. Freeze it. Fondant freezes very well and will keep for about 3 - 6 months. Make sure that you cover the extra fondant with vegetable shortening, wrap it 2 times with plastic wrap, and then put it into a freezer zip-top bag. Label it, then place in the freezer. This method can also be used for gum paste. The most important thing to remember if you are freezing both fondant and gum paste is to label the bags, you don't want to pull out the wrong item.
Round Cakes:
4 inch: 3/4 lbs
6 inch : 1 lb
8 inch: 1 1/2 lbs
10 inch: 2 lbs
12 inch: 3 lbs
14 inch: 4 lbs
16 inch: 5 lbs
Square Cakes:
4 inch: 1 lb
6 inch: 1 1/2 lbs
8 inch: 2 lbs
10 inch: 3 lbs
12 inch: 4 lbs
14 inch: 5 lbs
16 inch: 6 lbs
Hope this helps:)
Happy Caking!
Joan