I remember that newborn diapers did not last long and they grew out of them very quickly. You could probably go up a size anytime soon.

My son was 9lbs 2oz and birth and only wore newborn diapers for about 2 weeks before they just didn't fit right. Just be careful of the belly button with the size 1s. Fold the front down so it doesn't rub. Otherwise, it's perfectly fine to move up.

[johnreal]

I mostly depended on fitting. If the diaper seemed small, I'd get new ones the following day and put away the others (you never know when you'll need them again some day).

[gemmywilliams]

Hello
Depended ont he baby and their shape. Son, he ws bigger and stockier and a heavy eater/wetter, but I believe he was in them 1 month. Daughter was a 6 lb preemie and is petite now, slender, grew slowly so she wore newborn diapers for a couple months.