birth weight or present weight

A. hi well ,yes..as babies weight gain depends on their birth weight , we need both to check and ensure if child weighs enough or not but this is not big thing ,you can also check it by own too for that , the formula is your child should gain double his birth weight by the age of 6 months i am explaining it through example : suppose your child weight is 2 kg at birth time , so at 6 months age ,he should have weight around 4 to 6 kg.