One US quart is 0.946352946 litres, which means a litre is 1.0567 quarts. The two units are close enough that they are often treated as equivalent, and the six per cent gap is exactly the kind of difference that hides in plain sight.
About the units
The quart is a quarter of a gallon, which is where the name comes from. The US liquid quart is therefore 231 ÷ 4 = 57.75 cubic inches, or 32 US fluid ounces, or 2 US pints. The imperial quart is a quarter of an imperial gallon and comes to 1.1365 litres, twenty per cent larger. There is also a US dry quart, used for produce, which is 1.101 litres — a third value with the same name, arising because the American dry measures descend from the corn gallon rather than the wine gallon.
The exact factor
The exact value is 0.946352946 litres, derived from the gallon by dividing by four. The reciprocal, 1.05668820943, is the number of quarts in a litre. The practical consequence is that a litre bottle and a quart bottle look identical on a shelf and differ by about 54 ml, roughly three and a half tablespoons. In engine oil, where a car takes four or five quarts, the accumulated difference across a full change is around a quarter of a litre.
Where you meet this conversion
Engine oil and other automotive fluids, sold in quarts in the United States and litres almost everywhere else, with capacities printed in both in service manuals. Milk and juice cartons in the United States are quart and half-gallon sizes. In cooking, stock and soup quantities in American recipes are given in quarts, and pot sizes are described the same way. Laboratory and industrial supply catalogues serving both markets list both figures for what is often the same container.