| Reference | Gills (gi) | Nanoliters (nL) |
|---|---|---|
| A teaspoon | 0.0351951 gi | 5000000 nL |
| A can of soft drink | 2.32288 gi | 330000000 nL |
| A wine bottle | 5.27926 gi | 750000000 nL |
| A bathtub | 1055.85 gi | 1.5 × 1011 nL |
| An Olympic swimming pool | 17597540 gi | 2.5 × 1015 nL |
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 nanolitre is a unit of volume equal to one billionth of a litre, written nL. It is a thousandth of a microlitre, and a nanolitre of water has a mass of one microgram. It is the scale at which liquid handling stops being a matter of pipettes and becomes a matter of engineered channels, printed droplets and acoustic pulses.
Microfluidics is built here. A lab-on-a-chip moves samples through channels a few tens of micrometres wide, so the volume inside any one segment is measured in nanolitres, and a whole analysis may consume less than a microlitre. Working at this scale changes the physics as well as the quantity: surface tension dominates gravity, flows stay orderly rather than turbulent, and mixing has to be engineered rather than assumed.
Digital polymerase chain reaction shows what the scale buys. A sample is divided into around twenty thousand droplets of roughly one nanolitre each, every droplet is amplified separately, and the number that come out positive gives an absolute count of target molecules rather than a relative measurement. Dividing a microlitre into thousands of countable compartments is only possible because a nanolitre is small enough to hold either one target molecule or none.
Drug screening moves liquid without touching it. Acoustic dispensers use a focused sound pulse to eject droplets of two and a half nanolitres from an open well, with no tip and therefore no cross-contamination and no plastic waste. A screening plate of fifteen hundred wells can be filled with distinct compounds in a few minutes at this volume.
Printing and spotting work at the same magnitude. A microarray spot holds between half a nanolitre and five, an inkjet droplet is a few picolitres so a nanolitre is several hundred drops, and single-cell platforms encapsulate individual cells in droplets of this size because a mammalian cell occupies only a few picolitres.
Handling nanolitres reliably is mostly a fight against evaporation. A one-nanolitre droplet exposed to air can lose a measurable fraction of itself in seconds, so devices at this scale work under oil, in sealed channels or in humidity-controlled enclosures, and that constraint shapes the instruments more than the dispensing itself does.
One nanolitre equals 0.001 microlitres, 0.000001 millilitres, 0.001 cubic millimetres, or 1,000,000 cubic micrometres.