Free · Volume conversions

Metric & US Cups to Gallons Conversion Calculator

Convert metric & us cups to gallons with exact unit factors, editable results and an explained example.

  • Formula & worked example
  • Private in your browser
  • No signup
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

18.18436 metric cups = 1 imperial gallon = 4.54609 L. The starting cup is the 250 mL metric cup and the starting gallon is imperial. The selector also offers US customary and 240 mL US legal cups. A metric cup is not a historical imperial half-pint cup. Enter a known value in the units shown; editing a result solves the conversion in reverse.

18.18436 metric cups = 1 imperial gallon = 4.54609 L

Worked example

Enter these known values and leave the other values blank.

Volume in cups
18.18436 UK/AU/CA/ZA cups
Volume in gallons
1 UK gal
Volume in other units
4.546 L

Assumptions and limitations

  • The starting cup is the 250 mL metric cup and the starting gallon is imperial. The selector also offers US customary and 240 mL US legal cups. A metric cup is not a historical imperial half-pint cup.
  • The worked example uses the starting units. A unit selection preserves the quantity, so check the unit before entering a new number.
  • Where offered, a metric cup is 250 mL, a US legal cup is 240 mL, and the metric spoon choices are 5 mL and 15 mL. Fluid ounces measure volume rather than mass.

Common questions

Which volume convention does this conversion use?

The starting cup is the 250 mL metric cup and the starting gallon is imperial. The selector also offers US customary and 240 mL US legal cups. A metric cup is not a historical imperial half-pint cup.

How should I use a rounded result?

Keep enough digits for the accuracy of the original measurement. Display rounding changes the visible precision, while the calculation retains additional digits.

References

The US customary cup uses one sixteenth of the exact US liquid gallon, replacing the rounded captured cup volume. The US fluid ounce uses one 128th of the exact US liquid gallon, replacing the rounded captured reciprocal factor. Bookify replaces the captured rounded US gallon with the exact 3.785411784-liter definition.

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