A liter of water contains 4.23 cups in the U.S. standard measurement system. In the U.K. imperial measurement system, a liter contains 3.52 cups. A metric cup contains 250 milliliters, so there are precisely 4 metric cups in a liter.
If a person has a cup that is a non-standard form of measurement, such as a teacup or another drinking cup, measuring the volume of the cup determines how many of those cups are needed for 1 liter of water. He can divide 1,000 by the volume of the cup in milliliters to determine how many of these non-standard cups are in 1 liter of water.