it is 250 "ml" of semi skimmed as a Healthy Extra A. Although for alot of things ml's = the same in grams, it is not always the case, as ml's are volume and grams are weight. So you are better off measuring out 250ml in a jug.
But yes anything you use over that will need to be synned.
oops!!! so far i havent really been weighing out my milk, and i have been using it as a hex a every day since being on the plan.in a day i have a few teas and coffees with milk in, weetabix with milk in and often scrambled egg with bit of milk in too