I am making a 12" square cake and am trying to find out how much fondant will be needed. I found a chart for Wilton and one for Satin Ice but have noticed the amounts are considerably smaller on the Satin Ice chart. Does anyone have any suggestions on which might be right?

I've found the chart at earlenescakes.com very helpful in the past. It lists the amount you need to work with, and the amount that is usually covering the cake once you are done applying it and cutting off the excess. I've never used either of the others you mentioned, though.