From my calculations, once you've sewn a long strip of 2.5" strips together (how long we'll discuss in a minute), you look at building the depth of the blanket first. Your first strip is 2.5", 2" finished. When you fold that strip in half and sew, you end up with 4" finished. When you fold that strip in half and sew, you are now at 8" finished. Again, and you are at 16" finished, and again to 32". Now here's the biggie -- if you were to fold again, you'd be at 64" -- great for a lap quilt but huge for a baby.
If you stop at 32", then you need to decide what dimension you want the other side to be. Let's say you want a square -- then you need 16 x 32", or 512 inches of length, plus some extra for seam allowance. If you were using jelly roll strips of approximately 41", you'd need 13 of them (maybe 13 and a half of one, to be safe).
If you wanted it to be, say 32" x 40", then you multiple 16 x 40" for a total of 640 inches, which is about 16 strips, plus a half of one to get the staggered effect.
I hope this makes sense. I think the number of inches long can vary greatly, but the number of inches that accumulate in depth follows a certain pattern. I think you could use strips of fat quarters, too, as long as you have enough inches total in your first long strip.