One US pint is 0.4731764730 litres, about 473 ml. The imperial pint is 568 ml, twenty per cent larger, and that difference is the most widely noticed unit discrepancy in the English-speaking world because it is measured in beer.
About the units
The US pint is half a US quart, an eighth of a US gallon, and 16 US fluid ounces. The imperial pint is half an imperial quart, an eighth of an imperial gallon, and 20 imperial fluid ounces. Both descend from the same medieval unit but were fixed to different gallons — the American to the 231-cubic-inch wine gallon, the British to the ten-pounds-of-water imperial gallon of 1824. The twenty-ounce imperial pint against the sixteen-ounce American one is where the size difference comes from, compounded slightly by the fluid ounces themselves being different sizes in the opposite direction.
The exact factor
The exact value is 0.473176473 litres. The imperial pint is 0.56826125 litres. The ratio between them is 1.2009, the same 20 per cent that separates the gallons. In the United Kingdom the pint is one of the few imperial units still legally required for certain sales — draught beer and cider, and doorstep milk — which is why it survives while almost everything else went metric. A US pint of beer, at 473 ml, is closer to a European 500 ml glass than to a British pint.
Where you meet this conversion
Beer and cider above all, and the source of endless confusion for travellers. Also ice cream, which is sold in pints in the United States, and cream and berries in American grocery stores. Blood donation volumes are described in pints in American public messaging — a donation is about one US pint, 473 ml — while medical records use millilitres. Older British recipes call for pints of milk or stock, and using an American pint delivers 16 per cent less than intended.