| Reference | Gills (gi) | Kiloliters (kL) |
|---|---|---|
| A teaspoon | 0.0351951 gi | 0.000005 kL |
| A can of soft drink | 2.32288 gi | 0.00033 kL |
| A wine bottle | 5.27926 gi | 0.00075 kL |
| A bathtub | 1055.85 gi | 0.15 kL |
| An Olympic swimming pool | 17597540 gi | 2500 kL |
The gill is a unit of volume equal to a quarter of an imperial pint, or exactly 142.0653125 millilitres. Its symbol is gi. It is five imperial fluid ounces, and it sits between the fluid ounce and the pint in the old British liquid chain. Its name is pronounced with a soft g, so that it sounds like the name Jill, which surprises most readers who meet it only in print.
For most of the twentieth century it governed the British pub. Spirits were served in fractions of a gill, and the fraction varied by region: a sixth of a gill in England and Wales, a fifth in Scotland, and a quarter in Northern Ireland. A traveller ordering the same drink in three cities therefore received three different quantities, all legally correct and all described by the same words.
That system ended in 1995, when the United Kingdom replaced the gill fractions with metric measures of 25 or 35 millilitres, each establishment choosing one and displaying which. The change was less disruptive than it looked, because a fifth of a gill is 28.4 millilitres and a quarter is 35.5, so the new measures sat close to the old ones and the drinks barely changed size.
Cookery kept it longer than the law did. British and Irish recipes written before the 1970s call for a gill of cream, stock or milk, and the quantity is a quarter pint, which is 142 millilitres. Anyone working from an inherited recipe book meets the word regularly, and the conversion is one of the few worth writing on the flyleaf.
The American gill is a different quantity again. It is a quarter of a United States liquid pint, therefore four United States fluid ounces or 118.3 millilitres, about a sixth smaller than the imperial gill. It appears in old American recipes and in the occasional bar manual, and the same caution applies as with the pint: the name says nothing about which system is meant.
Today the gill survives in dialect, in historical writing and in the specifications of glassware sold for period use. It is one of the clearest cases of a unit outliving its own function, kept alive by cookbooks and by the memory of how a drink used to be poured.
One imperial gill equals 142.065 millilitres, 5 imperial fluid ounces, 0.25 imperial pints, or about 1.201 US gills.
The kilolitre is a unit of volume equal to one thousand litres, and therefore exactly one cubic metre. Its symbol is kL. The two names describe the same quantity, and which one appears depends entirely on the trade and the country: water utilities in the southern hemisphere say kilolitre where European ones say cubic metre.
Household water is where most people meet it. Australian, New Zealand and South African water bills are issued in kilolitres, tariffs are set as a price per kilolitre with rising blocks for heavier use, and drought restrictions are expressed as an allowance of so many kilolitres per household per quarter. A typical family uses between fifty and two hundred a year, so the annual bill fits in three digits.
Because the unit equals a cubic metre, it also carries an unusually direct physical meaning. A kilolitre of water weighs one tonne and would fill a cube one metre on each side, so a household allowance of a hundred kilolitres is a hundred tonnes of water, delivered, pumped and treated. Stating it that way is one reason the unit appears in conservation campaigns as often as on invoices.
Bulk liquid logistics uses it for cargo. A flexible tank fitted inside a shipping container carries around twenty-four kilolitres of wine, juice or edible oil, road tankers are rated in kilolitres, and depot storage is planned in thousands of them. Japanese petroleum statistics are published in kilolitres rather than in barrels, which makes Japanese energy figures awkward to compare with those of countries that use the barrel.
Industry generally prefers the cubic metre for the same quantity, because it is the coherent SI form and because it multiplies cleanly with metres of head, square metres of surface and other dimensional quantities. The kilolitre survives where the substance being measured is a liquid sold to the public, which is exactly where a name containing the word litre reads more naturally.
Converting is trivial in one direction and awkward in the other. One kilolitre is one cubic metre exactly and a thousand litres exactly, but 264.2 United States gallons and 220 imperial gallons, and about 6.29 barrels of oil, none of which are round numbers.
One kilolitre equals 1000 litres, 1 cubic metre, about 264.2 US gallons, or about 220 imperial gallons.