Hi....don't know if this helps but a charm pack usually consists of approx 40 x 5"x5" squares......what I realised a little while ago is that a layer cake consists of approx 40 x 10"x 10" squares ...... if you cut them in half and then in half again it will give you the equivalent to FOUR charm packs.......this is pretty obvious when you put as simple as that....just took me a while to realise !!!!......it is usually a lot cheaper to buy a layer cake that four charm packs.
Hope this helps