A US cup is a fixed volume: 1 US customary cup equals 236.588 ml, so 2 cups is about 473 ml. Most recipe writers round that to 475 ml, which is the usual metric-jug mark for it. Your jug will be accurate enough for milk in almost any recipe.
A quick note: this is the US cup. If the recipe came from the UK or Australia, a metric cup is 250 ml (Australia) and an imperial cup is about 284 ml, so check where the recipe was written if the dish is sensitive to proportions, like a custard or a batter.
For baking, measuring by weight is more precise than volume, but for milk the difference is small enough that a jug is fine.
