Water Converters
Convert common water volumes between litres, millilitres, US fluid ounces, US cups, and gallons. Choose the source unit carefully: US liquid gallons and UK Imperial gallons differ, and fluid ounces measure volume rather than weight.
Each converter shows its formula, a worked example, rounding behavior, and a source for the unit relationships. Cup tools identify the cup size used.
Litres and gallons
Litres to US Gallons
Convert litres to US liquid gallons; see the formula and how US and Imperial gallons differ.
Open converterUS Gallons to Litres
Convert a US liquid-gallon quantity to litres with clear unit labels.
Open converterImperial Gallons to Litres
Convert UK Imperial gallons to litres and compare the Imperial and US gallon sizes.
Open converterMillilitres and fluid ounces
Millilitres to US Fluid Ounces
Convert mL to US fluid ounces by volume—not ounces by weight.
Open converterUS Fluid Ounces to Millilitres
Convert US fluid ounces to mL for drink and container volumes.
Open converterCups
Cups to Millilitres
Choose a US customary cup or a recipe-defined 250 mL cup before converting.
Open converterMillilitres to Cups
Convert mL to cups with the cup size selected explicitly.
Open converterLitres to US Cups
Convert litres to US customary cups of 8 US fluid ounces.
Open converterCups to Litres
Convert cups to litres using the selected US or recipe-defined cup size.
Open converterReference chart
Water Volume Conversion Chart
Compare common water amounts across metric and US volume units.
Open converterChoosing the right unit
US and Imperial gallons
“Gallon” is ambiguous without a system. Select US liquid gallon for US measures and Imperial gallon for UK/Imperial measures.
Fluid ounces and ounces by weight
US fluid ounces measure volume. Ounces by weight measure mass; conversion between them also requires the substance’s density.
Cup sizes
These converters identify the US customary cup and offer a separate 250 mL option for recipes that explicitly define a cup that way. Follow the recipe’s stated measure.
Water calculator
For a separate rough daily fluid estimate, use the adult-oriented water calculator and review its method and limitations.
Open the water calculatorConversion references: NIST Guide to the SI, Appendix B.9 and NIST Metric Kitchen equivalencies. NIST publishes rounded conversion factors; converter outputs are also rounded for display.