Both my bubs varied what they drank so often that I just gave up even looking at how much they drank after a while. It sounds like she's recently had a bit of a growth spurt over the six week mark and after growth spurts, what they drink drastically decreases for a bit. Like the PP, the tin is only a guide but it definitely doesn't indicate what babies should be drinking. 180ml per feed is huge for an 8 week old. She might work her way up to that but don't stress that she's not finishing them. I definitely wouldn't change the formula that she's on if she's happy with it. It could only cause problems. How many feeds is she having a day? Maybe she wants to drop a feed......but then again she's still so little so I'd suggest just going by her cues. She obviously doesn't want anymore and she is obviously letting you know when she's hungry. As long as she's weeing a fair bit and is active and doesn't seem too lethargic, and she's putting on weight she's fine. There is a calculation that you can use to determine if they are drinking enough in a 24 hour period but honestly, I never used it because all it did was stress me out. You can't force them to eat if they don't want to. I accepted that eventually and just went with my DD's cues. It's hard to step back and just let them dictate how much they want when in the early weeks, it's all about amount of food, and weight gain. In the end, the amount of weight she is putting on will indicate to you whether she's getting enough. If you are worried, maybe just pop down to get her weighed. You'll probably find she's had a big gain recently and it will slow up a little after this 6 week growth spurt. I hope what I've said makes sense. I probably rambled a bit x