Conversion from 3 Cubic decimeters to US Liquid pints

Information about the Cubic decimeter (dm³)

The cubic decimetre is a unit of volume equal to one thousandth of a cubic metre, written dm³. It is the volume of a cube ten centimetres on each side, and since 1964 it has been the exact definition of the litre. The two are the same quantity, and the choice between them is the clearest example in the whole metric system of a name being chosen for what it does to a calculation.

Chemistry prefers the cubic decimetre for a specific reason. Concentration is written in moles per cubic decimetre, and every other quantity in the same calculation is expressed in metres, kilograms and seconds or their prefixed forms. Keeping volume as a length cubed means the units in an equation cancel by inspection, without anyone having to remember that a litre is a thousandth of a cubic metre.

That is why British and Commonwealth chemistry teaching writes mol dm⁻³ where American teaching writes molar. A one molar solution and a one mole per cubic decimetre solution are identical, but only the second form makes the dimensions visible. Students trained on it can check an answer by looking at the units, which is the most reliable error-catching habit in quantitative chemistry.

Gas volumes follow the same convention. One mole of an ideal gas occupies 22.4 cubic decimetres at zero degrees Celsius and one atmosphere, and about 24.0 cubic decimetres at room temperature, so a reaction stoichiometry converts to a measurable volume in one step. These are among the most quoted numbers in school chemistry, and they are almost always written in dm³ rather than in litres.

Elsewhere the litre wins easily. Nobody buys fuel, milk or paint in cubic decimetres, and no drink label carries the symbol, because the litre name is shorter, older and understood by everyone. The cubic decimetre survives where a formula rather than a customer is reading the number.

The relationship to its neighbours is worth keeping straight because of the cubing. A cubic decimetre holds a thousand cubic centimetres, not a hundred, and a thousand cubic decimetres make a cubic metre. Each step in length is a factor of ten and each step in volume a factor of a thousand, which is the source of most errors made with this unit.

One cubic decimetre equals 1 litre, 1000 cubic centimetres, 0.001 cubic metres, or about 61.02 cubic inches.

Information about the US Liquid pint (pt)

The United States liquid pint is a unit of volume equal to exactly 473.176473 millilitres. Its symbol is pt. It is sixteen United States fluid ounces and an eighth of a United States gallon. It is noticeably smaller than the imperial pint of 568 millilitres, because the American pint holds sixteen fluid ounces where the British one holds twenty.

That difference of four ounces is the whole story of the two pints. Both systems descend from the same medieval English measures, but Britain rebuilt its liquid chain in 1824 around a gallon of ten pounds of water, while the United States kept the older wine gallon of 231 cubic inches. The pint inherited the difference, and a British pint is now about a fifth larger than an American one.

The rhyme survives because the American pint fits it. A pint's a pound the world around works for the United States pint, since sixteen fluid ounces of water weigh 1.04 pounds, and it fails in Britain, where a pint of water weighs a pound and a quarter. The saying is a useful reminder that measurement rhymes travel worse than the measurements themselves.

Draught beer is where the difference becomes visible to travellers, and where American practice is looser than British. There is no federal requirement that a glass sold as a pint contain a pint, and the widely used sixteen-ounce shaker glass holds that volume only when filled to the brim, so a poured beer with a head contains less. Several states have legislated on the point precisely because the imperial system's verified glass has no American equivalent.

Domestic packaging uses it constantly. Milk, cream, ice cream and soft fruit are sold in pint containers, and a donated unit of blood is loosely called a pint although it is about 470 millilitres. Premium ice cream in a pint tub is one of the most recognisable retail formats in the country.

A separate United States dry pint of 551 millilitres exists for produce, and nothing in the word distinguishes it. A pint of cream and a pint of blueberries are therefore different quantities, differing by about sixteen per cent, which is the sort of detail that only becomes visible when someone tries to convert a recipe.

One United States liquid pint equals 473.176 millilitres, 16 US fluid ounces, 0.125 US gallons, or about 0.833 imperial pints.