What do u want to calculate? Only BM/ FM is allowed for NB. If FM, normally u can read at the packaging how many of oz of water n scoop of milk. N also gap of feeding. Basically NB, only 2oz of water with flat 2 scoop of milk. Than u have to gap in between 2-3 hours. But u have to refer back. Every brand of FM have slight change. BM u can just DF. Every 2 hours. Or whenever baby is crying.