How many oz?

We just made the switch from breast feeding to hypoallergenic formula a little over a week ago due to a dairy allergy. Everything I read says she should be eating 2.5oz per pound of weight. She is just over 11lbs but is only eating about 21oz a day. She appears full and satisfied, but of course, being a ftm, I question everything! Should I be encouraging her to eat more? Should I accept that she doesn't need as much? Is this common in babies that have recently switched from breast milk to formula? ANY advice is greatly appreciated!!