“Babies are more effective than pumps”. Does that mean baby is eating as much as I pump?

Hi all!

First time mom here with a 6 week old newborn who has been successfully breastfeeding from day one. He’s gaining really well so far so I know my milk is sufficient for him. As I prepare to return to work in 6 weeks, I’ve been pumping and giving 2 bottles a day to practice. He’s been taking 3oz bottles with success, but I’m wondering if that’s enough. I keep hearing LCs say “babies are more effective at removing milk than a breast pump”. I have a slight oversupply and pump between 4.5-8 ounces every time I pump to replace a feed, usually averaging around 5.5oz. Does that mean if my baby were to nurse for the same length of time that I pump, he’d be getting 5.5oz or more? Should I be giving more than 3oz bottles?

Sorry if this seems ramble-y. I have found the most challenging part of breastfeeding to be not knowing how much he’s getting and worrying if it’s enough.

Any advice is appreciated!