US and UK measures
A US gallon is 3.785411784 litres and a UK (imperial) gallon is 4.54609 litres, about 20% more. Pints differ the same way: 473 ml in the US, 568 ml in the UK. Recipes and fuel prices from the two countries use the same words for different amounts, so check where a figure came from. The cups, spoons and fluid ounces here are the US ones.
Cooking measures
1 US cup is 236.59 ml, 16 tablespoons or 48 teaspoons. A tablespoon is 14.79 ml and a teaspoon 4.93 ml. Many recipes round a cup to 240 ml and a tablespoon to 15 ml, which is close enough for cooking. Cups of flour or sugar into grams depends on the ingredient, so that cannot be done here.
Cubic units
A litre is a cubic decimetre, so 1,000 litres make a cubic metre. A cubic foot is 28.32 litres, the unit fridges, freezers and car boots are often sized in, and a cubic inch is 16.39 ml.
One pair at a time
The pairs people look up most have a page each, opened on that pair with a table of common values: ml to oz.
Questions
How many litres are in a gallon?
3.785 in a US gallon and 4.546 in a UK gallon. Going the other way, a litre is 0.264 US gallons or 0.220 UK gallons.
Is a millilitre the same as a cubic centimetre?
Yes, exactly: 1 ml is 1 cm³, which is why medicine and engine sizes are sometimes given in cc.