Question: how much should my baby gain by 1 month?
Answer: How Much Will My Baby Grow? The first month of life was a period of rapid growth. Your baby will gain about 1 to 1½ inches (2.5 to 3.8 centimeters) in length this month and about 2 more pounds (907 grams) in weight. These are just averages — your baby may grow somewhat faster or slower.