Formula milk amount

I have been putting formula powder into bottle before I put water and recently realise it's wrong 😭 Now I change to water first then powder but there's always a 20ml increase. If I make formula using 150ml water and it ends up as 170ml, do I count as my baby drink 150ml or 170ml if he finish? And if he don't finish and left 50ml, is it considered drink 170-50=120ml or 150-50=100ml? Thanks in advance! --- Edit: thanks everyone 🫶🏻