I would estimate 2-3 inches. my neice is 1 year, and her feet are 4 inches. But it's so hard to know. They will grow into them fast. I'd say make them long in the leg and go with about 3 inches. That way, worse come to worse, their an outer layer in cold weather that will be grown into quickly.

I just knit socks for my neice, and made them too small. I was shocked at how big her feet were. She's only a year, but her feet are big around, just short. When measured her feeat were almost 5 inches around and 4 long. Basicly, the measurements are the same though, and a standard leg is the same. Long legs are nice, as the kids find it harder to pull them off.

You should be able shorten the pattern to suit, my kids never fitted into the booties, they were always really big unless they were wearing the bonds suits.

Oh that does sound too long! What a lovely idea to have something to fit a newborn, I am sure she will be so  pleased! I don't remember exactly but the booties I kept are between two and three inches long. Maybe some new Mom's will answer! Happy crocheting!