| Milliliters (mL) | Cubic inches (in³) |
|---|---|
| 1 Milliliter | 0.0610237440947 in³ |
| 2 Milliliters | 0.122047488189 in³ |
| 3 Milliliters | 0.183071232284 in³ |
| 4 Milliliters | 0.244094976379 in³ |
| 5 Milliliters | 0.305118720474 in³ |
| 10 Milliliters | 0.610237440947 in³ |
| 20 Milliliters | 1.22047488189 in³ |
| 25 Milliliters | 1.52559360237 in³ |
| 50 Milliliters | 3.05118720474 in³ |
| 100 Milliliters | 6.10237440947 in³ |
| Reference | Milliliters (mL) | Cubic inches (in³) |
|---|---|---|
| A teaspoon | 5 mL | 0.305119 in³ |
| A can of soft drink | 330 mL | 20.1378 in³ |
| A wine bottle | 750 mL | 45.7678 in³ |
| A bathtub | 150000 mL | 9153.56 in³ |
| An Olympic swimming pool | 2.5 × 109 mL | 152559360 in³ |
The millilitre is a unit of volume equal to one thousandth of a litre, written mL or ml. It is exactly one cubic centimetre. It is the working unit of medicine, cookery, cosmetics and the laboratory, and it is the smallest volume most people handle deliberately in the course of a day.
Medicine relies on it more heavily than on any other unit of volume. Oral liquids are dosed in millilitres, syringes are graduated in them, intravenous fluids are prescribed as so many millilitres per hour, and blood test results are reported per millilitre or per decilitre. The precision matters: a tenfold dosing error in a paediatric prescription is a difference of a single decimal place in this unit.
That is why the household spoon has been driven out of medical instructions. A teaspoon is nominally five millilitres, but real spoons vary from two to nine, so dosing devices are now supplied with liquid medicines and marked in millilitres. Regulators in several countries require the millilitre marking precisely because it removes an ambiguity that spoons cannot.
Cooking outside the United States runs on it. European and Asian recipes give liquids in millilitres and litres rather than in cups, which is more precise because a cup measures volume by an unstandardised container while a millilitre does not. Wine and spirit measures, coffee shot sizes, and the capacity of a baby bottle are all specified in millilitres.
A convenient identity helps in the kitchen and the laboratory alike. One millilitre of water has a mass of one gram, so a recipe or a protocol can move between mass and volume for water-like liquids without a real error. Cosmetics use the same unit throughout, from a five-millilitre sample to a five-hundred-millilitre bottle.
Against United States and imperial measures it converts awkwardly, and the two differ from each other. One millilitre is 0.0338 United States fluid ounces but 0.0352 imperial fluid ounces, so a fluid ounce is about four per cent larger in Britain than in America, and any drink or medicine volume converted between them needs to state which system was meant.
One millilitre equals 1 cubic centimetre, 0.001 litres, about 0.0338 US fluid ounces, or about 0.0352 imperial fluid ounces.
The cubic inch is a unit of volume equal to 16.387064 cubic centimetres exactly. Its symbol is cu in, sometimes written in³. It is the volume of a cube one inch on each side, and 1728 of them make a cubic foot. Its most consequential role is legal rather than descriptive: the United States gallon is defined as exactly 231 cubic inches.
That definition is the reason American liquid measure is the shape it is. The figure of 231 comes from the English wine gallon standardised under Queen Anne in 1707, which the United States kept when Britain replaced its own gallons with a single imperial gallon in 1824. Every American fluid ounce, pint and quart descends from that one number, and it is why the two gallons differ by a fifth.
Engines made the unit famous. American car engines were quoted in cubic inches until the 1980s, and the numbers became names in their own right: a 350 is 5.7 litres, a 426 is 7.0, and a 302 is 4.9. Motorcycles still carry both figures, and the conversion is worth knowing, since 61 cubic inches make a litre.
Machinery uses it for swept volume. Pump and compressor displacement per revolution, hydraulic cylinder volume and metering pump strokes are all specified in cubic inches in American engineering, because the bores and strokes that produce them are already in inches and squaring or cubing an inch keeps the calculation in one system.
Freight pricing uses it in an unexpected way. American parcel carriers calculate a dimensional weight by dividing the package volume in cubic inches by a fixed divisor, commonly 139, to obtain a chargeable weight in pounds. A light bulky parcel is therefore priced by its cubic inches rather than by what it weighs, which changes how goods are packed.
The conversion to metric is exact but unhelpful. Because the inch is defined as exactly 2.54 centimetres, a cubic inch is exactly 16.387064 cubic centimetres, and no rounding is involved. That precision does not make the number easier to use, and it is the main reason engineering drawings outside the United States moved to millimetres.
One cubic inch equals 16.387 cubic centimetres, about 0.0164 litres, about 0.554 US fluid ounces, or 1/1728 of a cubic foot.