So say a king is 97 squared.
97" (length of quilt) divided by FINISHED strip width 2" = 49 (rounded up)
97" (width of quilt) x 49 strips long = 4753 inches
4753" divided by 40 (width of fabric est) = 119 strips plus 5 for extra(?)
I really like the idea someone posted elsewhere about adding a contrasting square to the end of each strip when first sewing them together end to end.
And definitely don't forget to chop off some from the first strip.