What is the measurement of 1 cup?
A US cup is 237 mL.

It is more practical to use grams though:
   256 grams of milk and 156 grams of oats.

WolframAlpha is the perfect place to look up these kind of things:

http://www.wolframalpha.com/input/?i=1+cup+of+oats

http://www.wolframalpha.com/input/?i=1+cup+of+milk