One liter has 1000 milliters. So logically while talking you can say that I liter is equal to 1000 ml and you don't use the term 1000 ml in one liter. But you can write the number of liters in milliliters like 1 milliliter = 0.001 litters. For more details, visit Litters, milliliters.

 0.001 because there are 1000 millis in a litre hence it's 0.001