As simple as..... One layer cake:
Equal 4 sets of charm squares:
I know. Obvious to everyone else. I'm making a butterfly quilt for my sister that requires 4 sets of charm squares. Brilliant me remembered at the last minute that equals a layer cake, which was cheaper (sometimes you can find good sales on them, especially on Etsy).
So, next time you begin one of those charm square projects, consider a layer cake instead.