Just had an e-mail asking me to figure this out for a BABY QUILT:
15 strips x 40" = 600" - 20" you cut from first strip = 580"
Fold once: 280" by 4" (I use finished sizes when I'm figuring it out)
Fold again: 140" by 8"
Fold again: 70" by 16"
Again: 35" by 32" (All of these are just approximate of course!)
You will be trimming a bit off the sides to even things up and then add borders so that it comes out
to the size you want. If you add 2" and 6" borders, that would bring it to a 48" x 48" size.