How much milk does a 18 month old baby need?

Hi,

Some researchers believe that at 5 months a baby should have minimal of 20oz of milk, other researchers believe that babies should drink the equivalent of their weight multiplies by 2 or 2.5 oz (ie) if your baby weighs 20 pounds, he/she should intake 40 oz... .

My son is also 5 months and used to drink over 40oz.. lately, he only drinks about 30 oz (he hasn't been interested in the bottle lately.. i hope its a phase and it will pass).