it depends on how big the carton is. If big then it would be in kg, if small then it would be grams.
what is the best estimate of the capacity of a soda can
If you're looking at a list of choices, I can't help you pick the best choice from the list because you're not sharing it. My estimate, without even seeing the small carton of milk, is 1 cup (8 fluid ounces, 1/2 pint).
Which is the best estimate of the mass of a small dog?
The one that's a small number of millliters, or an even smaller number of ounces.