Abi was gaining just over 1lb every 2 weeks and they said she was doing fine it's slowed down now to about 1lb every 3 weeks and she was breast fed, they say breast fed babies gain weight slower, i'd just do what you feel is right, nobody knows your child like you do, if he didn't want it he wouldn't take it.
found this
How much weight should I expect my breastfeeding baby to gain?
Breastfed and formula-fed babies grow at different rates. In general, breastfed babies tend to be leaner, which is healthier, especially in the long run. Here's a general guide to the growth of breastfed babies during the first year:
Weight gain of 4-7 ounces (112-200 grams) a week during the first month
An average of 1-2 pounds (1/2 to 1 kilogram) per month for the first six months
An average of one pound (1/2 kilogram) per month from six months to one year
Babies usually grow in length by about an inch a month (2.5c.m.) during the first six months, and around one-half inch a month from six months to one year.
and this
Amounts - How Much Per Feeding:
The average amount of formula (in ounces) that babies take per feeding usually equals the baby's weight (in pounds) divided in half (or equal to the weight in kg).
The average ounces of formula the baby takes in 24 hours is the baby's weight in pounds multiplied by 2 (or kg multiplied by 4).
A baby's appetite varies throughout the day. If the infant stops feeding or loses interest, the feeding should be stopped.
If your baby is healthy and not hungry at several feedings, increase the feeding interval.
The maximal amount of formula recommended per day is 32 ounces (1 liter).
Overfeeding can cause vomiting, diarrhea or excessive weight gain.
If your baby needs more than 32 ounces ( 1 liter) and is not overweight, start solids.
hope it helps