Depends if they’re formula or breast fed. Most pediatricians use American academy of pediatrics for reference and AAP says they should double birth weight by 4-6 months, and triple it by 1. So if they’re 6lbs at birth they should be 12lbs by 4-6months, and 18lbs by 1 year. Obviously every baby is different though!

They should gain a pound a month

There isnt one. All babies weigh differently.