Formula for 1 month old

Ericka

I recently started giving my one month old formula she was strictly breastfeeding but I noticed she wasnt getting enough so I switched. How often should i be giving her formula ? And how much ? I have been giving her about 2.5 to 3 oz. Like every 2 hours no sooner is that too much ? Or too little ? I still breastfeed her at night.