Water Unit Converter
Instantly convert any volume of water between litres, millilitres, US and Imperial gallons, cups and fluid ounces — with every unit shown at once.
Also shows the value in every unit for a quick full picture.
Educational estimates only — not medical, engineering or professional advice.
Water volumes appear in a bewildering variety of units depending on where you are in the world and what you are reading — a nutrition label, a plumbing manual or a recipe. This converter bridges them all.
Choose a starting value and unit, select where you want to end up, and the result appears immediately. A full breakdown across all six units is shown below, so you rarely need to convert twice.
How to use this tool
Pick the amount you know, the unit it is in, and the unit you want. The converter uses millilitres as the internal reference:
- 1 litre = 1,000 mL
- 1 US gallon = 3,785.41 mL
- 1 Imperial gallon = 4,546.09 mL
- 1 Cup = 250 mL (as used on this site)
- 1 US fluid ounce = 29.5735 mL
A little background
The US gallon and the Imperial (UK) gallon are different volumes — a point that causes frequent confusion. The Imperial gallon is about 20 % larger. The same gap applies to their derived units such as pints and fluid ounces.
Cups are not standardised globally, but the 250 mL definition used here matches Australian and Canadian nutrition labelling and is the most widely agreed value for everyday use.