| Cubic feet (ft³) | Microliters (µL) |
|---|---|
| 1 Cubic foot | 28316846.59 µL |
| 2 Cubic feet | 56633693.18 µL |
| 3 Cubic feet | 84950539.77 µL |
| 4 Cubic feet | 113267386.36 µL |
| 5 Cubic feet | 141584232.95 µL |
| 10 Cubic feet | 283168465.9 µL |
| 20 Cubic feet | 566336931.8 µL |
| 25 Cubic feet | 707921164.75 µL |
| 50 Cubic feet | 1415842329.5 µL |
| 100 Cubic feet | 2831684659 µL |
| Reference | Cubic feet (ft³) | Microliters (µL) |
|---|---|---|
| A teaspoon | 0.000176573 ft³ | 5000 µL |
| A can of soft drink | 0.0116538 ft³ | 330000 µL |
| A wine bottle | 0.026486 ft³ | 750000 µL |
| A bathtub | 5.2972 ft³ | 150000000 µL |
| An Olympic swimming pool | 88286.7 ft³ | 2.5 × 1012 µL |
The cubic foot is a unit of volume equal to 1728 cubic inches, or 28.3168 litres. Its symbol is cu ft, sometimes written ft³. It is the volume of a cube one foot on each side, and it is the unit in which the United States measures natural gas, appliance capacity and air flow, three fields with almost nothing else in common.
Natural gas is its largest use by far. American gas meters record consumption in hundreds of cubic feet, bills are issued in thousands, and national reserves are quoted in trillions. Because the energy in a given volume of gas depends on its composition, utilities also publish a heating value per cubic foot, and the bill is the product of the two.
Appliances are sized in it. Refrigerator and freezer capacity in the United States is quoted in cubic feet, so a family refrigerator is about twenty and a chest freezer perhaps seven, and the same convention covers microwave ovens, washing machines and truck cargo boxes. Shoppers compare products by a number that describes usable space rather than external dimensions, which is genuinely more useful.
Air movement uses it per unit time. Fans, extractors, air conditioners and compressors are rated in cubic feet per minute, a figure abbreviated to CFM in every American catalogue. Ventilation standards are written as required air changes, which convert to cubic feet per minute once the room volume is known, so the unit sits on both sides of the calculation.
Materials and freight follow the same scale. Concrete, gravel, mulch and topsoil are sold by the cubic foot in smaller quantities and by the cubic yard in larger ones, twenty-seven cubic feet making one cubic yard. A cubic foot of fresh water weighs 62.4 pounds and holds about 7.48 United States gallons, which are the two figures most often needed alongside it.
Its metric equivalent is not memorable, at 28.3168 litres or 0.0283 cubic metres, and neither is its relationship to the cubic inch, at 1728. Those factors are why engineering outside the United States moved to metric volumes early even where lengths stayed imperial for longer.
One cubic foot equals 1728 cubic inches, about 28.317 litres, about 7.48 US gallons, or about 0.0283 cubic metres.
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.