How many ml in one part?

Answer 1

There is no given measure for a part. The measure to use is dependent on the measure used for other "parts".

2 parts water to 3 parts flour and 1 part sugar, will give you a consistent batter despite the measure used. It could be tablespoons to get a 3 ounce amount of batter, cups to get 3 pints of batter, gallons to make 6 gallons of batter and so on. Parts indicates that each amount is relative to the other parts. Parts usually imply a volume measure, not a weight measure.