Stopping formula nearer 12 months

My son is 10 months so I'm planning on continuing formula for another 2 months and then changing to cows milk. I feel now he's weaning himself off his formula. He's down to 2 9oz bottles daily which fits the 18oz recommendation in the UK however now hes not always finishing them meaning some days he can have as little as 14oz. Is this ok if he's having 3 meals and eats well? Also for example if I make a 6oz bottle with 6 scoops formula this fills the bottle to 7oz. How many oz would you say baby has had?