Baby drink lesser than she supposed to be?

Mummies i wanna ask ur opinion Baby weight now 5.5kg so by right she shd drink 5.5x150ml = 825ML per day - correct? But my LO only drink 600ish per day (including dream feed) (formula milk) Btw it has been going for 3 weeks. The amount of milk quite consistent Is this something i shd be worried about?