How many inches across is your standard adult-size afghan?
The difficulty is that for some people, an afghan is something you throw across your lap when you’re chilly, and for some it’s something that covers your bed. I checked my copy of Nicky Epstein’s book [I]Knitting for Your Home[/I]. The afghan projects range in width from 40 1/2 inches to 60 inches. If you want it to cover a bed, all you’d need to do is measure the width of the mattress, then add the number of inches you want it to hang over the edge x 2.