They say between 6 to 8 oz a week is average, but all babies are different, Charlie was 7lbs 13 when he was born and at 4 weeks was 10lb 5 and now at 15 weeks weighs 15lbs 6. He is a very chunky munky, my sister n law has a little girl who was 7lbs 9 oz when born and 11 weeks on is only 10lbs 13 oz so it just shows you there is no such thing as normal its all down to the individual baby.