Conversion from US Liquid pints to Gigaliters

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.

Information about the Gigaliter (GL)

The gigalitre is a unit of volume equal to a billion litres, or one million cubic metres. Its symbol is GL. It is also exactly one cubic hectometre, which is the same quantity written in coherent SI form. It is the unit in which reservoirs, catchments and national water plans are counted, and it is where water measurement stops describing supply and starts describing landscape.

Dam storage is its principal use. Australian reservoir levels are published in gigalitres and as a percentage of a stated capacity in the same unit, so a city's water security can be read as a single number that changes week by week. Warragamba Dam, which supplies most of Sydney, holds a little over two thousand gigalitres when full, and the whole system a few hundred more.

Policy is written in it as well. The Murray-Darling Basin Plan set out to recover water for the environment in gigalitres, and every argument about that plan has been an argument about how many gigalitres should come out of irrigation and go back into rivers. Desalination plants are rated the same way: a large plant produces something like ninety gigalitres a year, which is a meaningful fraction of a city's demand.

Australians have an informal comparison for it. The volume of Sydney Harbour is taken as roughly five hundred gigalitres, and flood volumes, storage losses and river flows are described in harbours as casually as elsewhere they are described in swimming pools. Two thousand Olympic pools make one gigalitre, which is the more portable comparison for readers elsewhere.

The unit's identity with the cubic hectometre is worth holding on to. Spanish and Latin American hydrology publishes reservoir capacity in cubic hectometres, so a Spanish figure of 500 hm³ and an Australian figure of 500 GL describe exactly the same body of water, and any comparison between the two systems needs no arithmetic at all.

Above the gigalitre, water quantities pass to the cubic kilometre, which is a thousand of them, and are used for lakes, ice sheets and global budgets rather than for anything a government can manage. Below it, the megalitre takes over for individual farms, works and pipelines.

One gigalitre equals 1,000,000,000 litres, 1,000,000 cubic metres, 1 cubic hectometre, or about 264 million US gallons.