how much does your baby take from a bottle

For moms who breastfeed and give bottles. When giving your little one a bottle how much do they take? And how often like when they're at daycare? My little is four months and on a good day he takes 4 oz every three hours. We just had his four month appointment and he has not gained weight since the last appointment (15lbs). I would love yours opinion and support. Also when nursing he nurses 10 minutes each side and every three hours.thanks in advance.