Chart of average weightsAge50th percentile weight for male babies50th percentile weight for female babies3.5 months14.1 lbs. (6.4 kg)13 lbs. (5.9 kg)4.5 months15.4 lbs. (7.0 kg)14.1 lbs. (6.4 kg)5.5 months16.8 lbs. (7.6 kg)15.4 lbs. (7.0 kg)6.5 months18 lbs. (8.2 kg)16.5 lbs. (7.5 kg)