A quick answer is that 1 liter of milk is approximately 4.227 cups. To be more precise, since 1 liter equals 1000 milliliters, and 1 cup in the US customary system is equal to 236.588 milliliters, one liter converts to 4.22675 cups.

## Detailed Explanation

When converting between metric and US customary units, it is important to know the exact definitions of each unit. Let’s break this down step-by-step:

- 1 liter is exactly equal to 1000 milliliters. This is by definition of the metric system.
- 1 US cup is defined as exactly 236.588 milliliters. This is a legally defined conversion factor in the US customary system.
- To convert liters to cups, we set up a simple proportion:
- 1 liter = 1000 milliliters
- x cups = 236.588 milliliters

- Cross-multiplying gives:
- x = (1000 milliliters * x cups) / 236.588 milliliters
- x = 4.22675 cups

Therefore, one liter of volume is equal to 4.22675 cups in the US customary system. The conversion factor between liters and US cups is 1 liter = 4.22675 cups.

## Why the odd conversion factor?

You may wonder why the US cup is defined as 236.588 milliliters, rather than a round number like 250 mL or 200 mL. This has to do with the history of the US customary system.

The US customary units like cups, fluid ounces, pints, quarts, and gallons can be traced back to the British Imperial system used in the 18th and 19th centuries. In 1824, the British Parliament standardized a system of Imperial measurements, which defined the gallon as the unit of volume and set it equal to 277.274 cubic inches. The cup was then defined as 1/16 of a gallon.

Based on the gallon definition, the math works out to:

- 1 gallon = 277.274 cubic inches
- 1 cup = 1/16 gallon = 277.274/16 cubic inches = 17.28125 cubic inches
- 17.28125 cubic inches = 236.588 milliliters

When the US Customary System was developed, it kept the same definition of the cup for historical continuity with the British Imperial System. So while the cup measurement seems very odd in the metric system, its origins make more sense when traced back to the original Imperial gallon definition.

## Cups to Liters Conversion Table

Here is a table showing some common conversions between cup measurements and liters:

Cups | Liters |
---|---|

1 cup | 0.24 liters |

2 cups | 0.47 liters |

3 cups | 0.71 liters |

4 cups (1 quart) | 0.95 liters |

8 cups (1/2 gallon) | 1.9 liters |

16 cups (1 gallon) | 3.8 liters |

## Conversion When Cooking

For practical purposes, most recipes and kitchen measurements will round 1 liter to 4 cups. However, it’s good to know the exact conversion factor for accuracy in certain cases. For example, when developing recipes it’s important to use the precise definition of cups and liters.

When doing casual cooking and measuring in the kitchen, either round 1 liter to 4 cups OR measure it out exactly using a measuring cup that has been calibrated to the legal US cup definition. Most standard kitchen cup measures use the exact 236.588 mL conversion factor.

So for simplicity, you can measure out 4 cups of milk using a kitchen measuring cup and know that it very closely equals 1 liter. However, to be technically accurate, use the conversion factor of 1 liter = 4.22675 cups.

## Conclusion

In summary, one liter of liquid volume is equal to 4.22675 cups in the US customary system. This odd conversion comes from the historic definition of the US gallon, which was carried over from the British Imperial system in the 1800s. For general kitchen use, rounding 1 liter to 4 cups is fine. But for precision measurements, use the exact conversion factor of 4.22675 cups per liter.