Depends on age
Initially breastfed babies tend to lose weight
but once mom's milk comes in they should gain about 30g (1 oz) a day! from 3-6 months they gain about 20 grams a day, after 6 months they gain about 10g (1/3 of an ounce) a day.
Toddlers gain 5 lbs/yr. These are averages. The most important thing is that your baby is growing along his growth curve; your pediatrician will help make sure he's on track.