Volume conversions trip people up because the same names mean different amounts: a US gallon is 3.785411784 liters but an imperial (UK) gallon is 4.54609 liters, and a US fluid ounce is slightly larger than an imperial one. This page labels every unit explicitly. Kitchen units follow the US customary system (1 cup = 8 fl oz = 16 tablespoons = 48 teaspoons); metric cups of 250 mL are used in Australia, Canada and New Zealand.
Use the converter above for any pair. The most searched kitchen and fuel conversions have their own pages with worked examples and quick-reference tables, listed above.