Figuring Quantity of Fabric for Bargello
 

My latest vision is to make window quilts in a bargello pattern for the 3 windows across my living room...DH has the blinds drawn all the time anyway to keep the glare off the tv. And the blinds were here when we bought the house and leave a lot to be desired.

Are there any general rules of thumb for figuring it out? I could (and probably should) sketch out what I want and add up the number of strips.