My baby is 6 weeks old and has been eating around 3.5-4oz per feed since around 4 weeks. Every baby is different! My advice would be to just pump 3-4oz, and see when he gets full, or if he needs more. That way you know approximately how much you need for next time!
If you are pumping the "extra" after a feeding, it will probably take a couple pump sessions to make one bottle. Aim for about 4 oz for a full bottle. Make sure your flanges are sized correctly and pump for about 10 minutes. Start with faster suction in "let down" mode then once things are flowing, switch to slower suction "expression" mode. Remember that after a feeding you're "putting in and order for later" or getting out the "extra" baby didn't remove, so don't be discouraged by small output
@Charlotte say I do a few oz over a couple of hours, can I mix that milk together? Xx
@Zara Yup! It's called the pitcher method or pooling method. Check out this story highlight from Karrie Locher for more info on it: https://www.instagram.com/s/aGlnaGxpZ2h0OjE3OTI1NTQ1MjI1MTU2Nzcw?story_media_id=2807178137662061686_180710211&igsh=MWdhbzZreGQ0cDA1dg==
Each baby is different, I'd start with a small amount like 50ml and give a boob top up after, increasing to about 100ml when you can over a few days of pumping n see where your baby is at in regards to wanting more or not drinking it all. Collecting the initial amount little and often. You'll find your own rhythm. Pumping at night is good as that's when your body resets your milk amount produced, normally I pump a bottle as hubby feeds a bottle now. Our 8 week old is having 130-150ml at the moment. Good luck
My baby was eating 2.5-3oz every 2-3 hours at that age. It really depends on the baby though