How many cups are in 1200ml depends on whether you are using US measurements or UK measurements, as there is a slight difference between the two.
If you are using UK measurements, where 1 cup is equal to 250ml, then 1200ml is equal to 4.8 cups, or 4 and four-fifths cups.
As a general rule, if you have a US recipe and you are used to British measurements, remove 2 teaspoons of liquid per US cup to make it a British 'cup'.
Why the Difference?
This stems from a US pint being 16 fluid ounces rather than 20 fluid ounces, as it is in the UK. Cups are also used to measure weight in US recipes, which makes things even trickier - a cup of flour will weigh a different amount to a cup of sugar! Luckily, you can purchases US measuring cups from numerous online stores.
Here's one such product which solves the problem: