| Hectoliters (hL) | Microliters (µL) |
|---|---|
| 1 Hectoliter | 100000000 µL |
| 2 Hectoliters | 200000000 µL |
| 3 Hectoliters | 300000000 µL |
| 4 Hectoliters | 400000000 µL |
| 5 Hectoliters | 500000000 µL |
| 10 Hectoliters | 1000000000 µL |
| 20 Hectoliters | 2000000000 µL |
| 25 Hectoliters | 2500000000 µL |
| 50 Hectoliters | 5000000000 µL |
| 100 Hectoliters | 10000000000 µL |
| Reference | Hectoliters (hL) | Microliters (µL) |
|---|---|---|
| A teaspoon | 0.00005 hL | 5000 µL |
| A can of soft drink | 0.0033 hL | 330000 µL |
| A wine bottle | 0.0075 hL | 750000 µL |
| A bathtub | 1.5 hL | 150000000 µL |
| An Olympic swimming pool | 25000 hL | 2.5 × 1012 µL |
The hectolitre is a unit of volume equal to one hundred litres, or a tenth of a cubic metre. Its symbol is hL. It is the trading unit of the drinks industry and of much of agriculture, and although almost nobody outside those trades ever writes it, within them it is the number that appears on every contract, licence and annual report.
Brewing runs on it entirely. A brewery's capacity is stated in hectolitres a year, duty is assessed on hectolitres produced, and the large international groups report annual volumes in hundreds of millions of them. A standard keg holds half a hectolitre, so the unit also happens to match the physical container the trade moves, which is part of why it stuck.
Wine regulation is written in the same terms. European appellation rules cap yield in hectolitres per hectare, a figure that does more than any other single number to define the character of an appellation, since a low cap concentrates the fruit and a high one dilutes it. Production statistics, stocks and the surpluses that periodically trouble the European market are all counted the same way.
Grain trading uses the unit in an unexpected direction. The hectolitre weight, or test weight, is the mass of grain that fills one hectolitre, and it is a standard quality specification: milling wheat is typically bought at 76 to 80 kilograms per hectolitre, and a load below the contracted figure is downgraded. The measurement works because well-filled, undamaged grain packs more densely than shrivelled grain does.
Dairy and other bulk liquids follow. Milk collection, fruit juice processing, edible oil and cider are all recorded in hectolitres, because the quantities involved are too large for litres to read comfortably and too small for cubic metres to be precise enough for duty and quality purposes.
For scale, a hectolitre is a large domestic water tank, a household bath filled about one and a half times, or a barrel of oil and a half. It converts to 22 imperial gallons or 26.4 United States gallons, and to 0.1 cubic metres exactly, which is the quickest route into SI-based calculations.
One hectolitre equals 100 litres, 0.1 cubic metres, about 26.4 US gallons, or about 22 imperial gallons.
The microlitre is a unit of volume equal to one millionth of a litre, written µL. It is exactly one cubic millimetre. It is the working unit of the molecular biology laboratory and of clinical haematology, and almost every quantity in modern biological science that is not a mass or a concentration is a number of microlitres.
Pipetting is what defines it in practice. Adjustable micropipettes are named after their maximum volume in microlitres, so a bench holds instruments of 2, 20, 200 and 1000, and a researcher's day consists largely of moving microlitres from one tube to another. A polymerase chain reaction is typically assembled in twenty to fifty microlitres, and a whole experiment may use less liquid than a teaspoon holds.
Blood counts are reported against it. White cells number between four thousand and eleven thousand per microlitre in a healthy adult, platelets between a hundred and fifty thousand and four hundred thousand, and red cells about five million. Those reference ranges are among the most widely used numbers in medicine, and all of them are counts within a cube one millimetre on a side.
Diagnostics has driven the volumes down. A modern blood glucose meter needs about half a microlitre of blood, which is why a finger-prick sample is enough where an earlier generation of instruments needed a syringe. Point-of-care analysers, lateral flow tests and microfluidic cartridges are all designed around the smallest sample a patient can be asked to give.
Analytical chemistry uses the same scale. Injection volumes in liquid chromatography run from one to twenty microlitres, gas chromatography uses one or less, and mass spectrometry samples are prepared in tens. Because the analytical signal depends on the amount injected, the accuracy of a microlitre-scale measurement sets the accuracy of the whole result.
The identity with the cubic millimetre is a genuine convenience. Haematology once reported cell counts per cubic millimetre and now reports them per microlitre, and the numbers did not change at all, because the two units are the same. That is a rare case of a unit change in medicine that required no re-education and produced no errors.
One microlitre equals 1 cubic millimetre, 0.001 millilitres, 0.000001 litres, or about 0.0000338 US fluid ounces.