| Gills (gi) | Megaliters (ML) |
|---|---|
| 1 Gill | 0.0000001420653125 ML |
| 2 Gills | 0.000000284130625 ML |
| 3 Gills | 0.0000004261959375 ML |
| 4 Gills | 0.00000056826125 ML |
| 5 Gills | 0.0000007103265625 ML |
| 10 Gills | 0.000001420653125 ML |
| 20 Gills | 0.00000284130625 ML |
| 25 Gills | 0.0000035516328125 ML |
| 50 Gills | 0.000007103265625 ML |
| 100 Gills | 0.00001420653125 ML |
| Reference | Gills (gi) | Megaliters (ML) |
|---|---|---|
| A teaspoon | 0.0351951 gi | 0.000000005 ML |
| A can of soft drink | 2.32288 gi | 0.00000033 ML |
| A wine bottle | 5.27926 gi | 0.00000075 ML |
| A bathtub | 1055.85 gi | 0.00015 ML |
| An Olympic swimming pool | 17597540 gi | 2.5 ML |
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 megalitre is a unit of volume equal to one million litres, or one thousand cubic metres. Its symbol is ML. It is the working unit of water management: irrigation entitlements, treatment works capacity, farm dams and the trading of water rights are all counted in megalitres, because the quantities involved are far too large for litres and awkwardly small for cubic kilometres.
Australia has made the most of it. Irrigation water in the Murray-Darling Basin is held as entitlements measured in megalitres, seasonal allocations are announced as a percentage of those entitlements, and the resulting rights are traded on an open market where prices are quoted in dollars per megalitre. That market is among the largest of its kind in the world, and every price in it is a price per million litres.
British water utilities use it for throughput. A treatment works is rated in megalitres per day, distribution zones are balanced in the same unit, and leakage is reported as megalitres lost daily across a network. Because a large city consumes several hundred megalitres a day, the unit keeps national and regional figures in three or four digits rather than in unreadable strings of zeros.
A familiar object fixes the scale. An Olympic swimming pool of fifty metres by twenty-five, filled to two metres, holds 2500 cubic metres, which is two and a half megalitres. Journalism uses that comparison constantly for reservoir levels and flood volumes, and it works precisely because the pool and the unit are within a factor of three of each other.
On farms the unit describes storage. An Australian farm dam might hold anything from five to fifty megalitres, an on-farm irrigation season is planned in megalitres per hectare, and evaporation losses from open storage are estimated the same way. Sewage treatment, industrial process water and mine site water balances all follow.
Its one hazard is typographic. In the correct symbols, mL is a millilitre and ML is a megalitre, and the two differ by a factor of a thousand million. A document that is careless about capitals can therefore turn a laboratory volume into a reservoir, which is why water and clinical writing both insist on the case being right.
One megalitre equals 1,000,000 litres, 1000 cubic metres, about 264,172 US gallons, or about 220,000 imperial gallons.