Conversion from 2 Microliters to Fluid ounces

Information about the Microliter (µL)

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.

Information about the Fluid ounce (fl oz)

The fluid ounce in the imperial system is a unit of volume equal to exactly 28.4130625 millilitres. Its symbol is fl oz. Twenty of them make an imperial pint and 160 an imperial gallon. It is the smallest unit of the imperial liquid chain in ordinary use, and its name records exactly what it was built to do.

The name is literal. The Weights and Measures Act of 1824 defined the fluid ounce as the volume occupied by one avoirdupois ounce of water, so a fluid ounce of water weighs an ounce. The modern definition is metric and the agreement is no longer exact, but it is close: a fluid ounce of water weighs 28.4 grams against the ounce's 28.35, a difference of two parts in a thousand.

The United States fluid ounce is a different quantity, and the relationship between the two is the most confusing pair of units in either system. A United States fluid ounce is 29.5735 millilitres, so it is four per cent larger than the imperial one. Yet a United States pint contains only sixteen of them where an imperial pint contains twenty, so the American pint ends up seventeen per cent smaller. The smaller unit belongs to the larger system and the larger unit to the smaller.

That reversal has practical consequences. A recipe calling for eight fluid ounces of milk means 237 millilitres in America and 227 in Britain, which is tolerable, but one calling for a pint means 473 or 568, which is not. Cosmetics, medicines and drinks all carry both figures on internationally sold packaging for exactly this reason.

British labelling now leads with millilitres. Toiletries, spirits and soft drinks are specified in metric units, with fluid ounces printed alongside for markets that expect them, and pharmacy long ago abandoned the fluid ounce and the fluid dram in favour of millilitres. What survives is culinary and conversational rather than legal.

Where an old British recipe uses it, the conversion is straightforward as long as the system is known: multiply by 28.4 for millilitres, and remember that the pint above it holds twenty and not sixteen. Getting the pint right matters more than getting the ounce right, because the error compounds with quantity.

One imperial fluid ounce equals 28.4130625 millilitres, 1/20 of an imperial pint, or about 0.961 US fluid ounces.