I've had four children. My oldest was 6lbs when she was born. She wore newborns for maybe 2 months. My other three were 7lbs, 7lbs1oz and 7lbs 14oz, they all wore newborns for about a month. Newborns go through maybe 10 diapers a day, especially if you're planning to breastfeed! A box of newborn diapers has 88. Sooo 1 box would get you through roughly a week.
Definitely don't buy too many newborn diapers, I'd say start with one box of 88 count and if baby still fits them after that you can buy more. My baby started out wearing size one, I would buy 2-3 large boxes of size 1
And they give you a guide @ BABIES R US TOO! So you can plan accordingly! Also, if you dont use a pack, box, case they will exchange it for the size you need!
If you do it threw toys r us do a bunch of each even if ppl don't buy them all you get points and gift cards in the mail the more you spend on your registry so even after your little ones here buy off the registry and you earn points
I put a variety of sizes on my registry and variety of brands too! it's hard not knowing what baby will be best with!