| Reference | Gills (gi) | Cubic centimeters (cm³) |
|---|---|---|
| A teaspoon | 0.0351951 gi | 5 cm³ |
| A can of soft drink | 2.32288 gi | 330 cm³ |
| A wine bottle | 5.27926 gi | 750 cm³ |
| A bathtub | 1055.85 gi | 150000 cm³ |
| An Olympic swimming pool | 17597540 gi | 2.5 × 109 cm³ |
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 cubic centimetre is a unit of volume equal to one millionth of a cubic metre, written cm³ and often abbreviated cc. It is the volume of a cube one centimetre on each side, and since the litre was redefined in 1964 it is exactly one millilitre. The two names describe the same quantity, but they belong to different trades and are not interchangeable in every context.
Engines are its most visible home. Motorcycle and small-engine displacement is quoted in cubic centimetres, so a 125, a 600 and a litre bike are named by the swept volume of their cylinders. Licence categories in much of the world are drawn on the same scale, with a 125 cc limit for learners in many European countries, which turns the unit into a legal boundary rather than a mere description.
Car engines cross over to litres at about a thousand cubic centimetres, purely for readability, so a 1998 cc engine is advertised as a two-litre. American practice used cubic inches for the same purpose well into the 1980s, and the conversion is worth knowing: 1000 cubic centimetres is 61 cubic inches, so a 350 cubic inch engine is 5.7 litres.
Medicine has deliberately retreated from the abbreviation. Syringes were once marked in cc and clinicians spoke that way, but handwritten cc can be misread as a unit symbol or as a pair of zeros, and medication safety bodies now place it on lists of abbreviations that should not be used. The instruction is to write mL instead, even though the quantity is identical.
Materials science keeps the unit for density. Grams per cubic centimetre is the standard way to state how heavy a substance is for its size: water is 1.00, aluminium 2.70, steel about 7.85, lead 11.34 and gold 19.3. Those numbers are memorable precisely because the cubic centimetre is small enough that everyday solids land between one and twenty.
Modelling and manufacturing use it for part volume. Computer-aided design reports the volume of a component in cubic centimetres, which converts directly to mass once a density is chosen and to material cost in additive manufacturing. It is the natural unit for anything that fits in a hand.
One cubic centimetre equals 1 millilitre, 1000 cubic millimetres, 0.000001 cubic metres, or about 0.061 cubic inches.