| Fluid ounces (fl oz) | Cubic centimeters (cm³) |
|---|---|
| 1 Fluid ounce | 28.4130625 cm³ |
| 2 Fluid ounces | 56.826125 cm³ |
| 3 Fluid ounces | 85.2391875 cm³ |
| 4 Fluid ounces | 113.65225 cm³ |
| 5 Fluid ounces | 142.0653125 cm³ |
| 10 Fluid ounces | 284.130625 cm³ |
| 20 Fluid ounces | 568.26125 cm³ |
| 25 Fluid ounces | 710.3265625 cm³ |
| 50 Fluid ounces | 1420.653125 cm³ |
| 100 Fluid ounces | 2841.30625 cm³ |
| Reference | Fluid ounces (fl oz) | Cubic centimeters (cm³) |
|---|---|---|
| A teaspoon | 0.175975 fl oz | 5 cm³ |
| A can of soft drink | 11.6144 fl oz | 330 cm³ |
| A wine bottle | 26.3963 fl oz | 750 cm³ |
| A bathtub | 5279.26 fl oz | 150000 cm³ |
| An Olympic swimming pool | 87987699 fl oz | 2.5 × 109 cm³ |
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.
The cubic centimetre is a unit of volume equal to one millionth of a cubic metre, written cm³ and often abbreviated cc. It is the volume of a cube one centimetre on each side, and since the litre was redefined in 1964 it is exactly one millilitre. The two names describe the same quantity, but they belong to different trades and are not interchangeable in every context.
Engines are its most visible home. Motorcycle and small-engine displacement is quoted in cubic centimetres, so a 125, a 600 and a litre bike are named by the swept volume of their cylinders. Licence categories in much of the world are drawn on the same scale, with a 125 cc limit for learners in many European countries, which turns the unit into a legal boundary rather than a mere description.
Car engines cross over to litres at about a thousand cubic centimetres, purely for readability, so a 1998 cc engine is advertised as a two-litre. American practice used cubic inches for the same purpose well into the 1980s, and the conversion is worth knowing: 1000 cubic centimetres is 61 cubic inches, so a 350 cubic inch engine is 5.7 litres.
Medicine has deliberately retreated from the abbreviation. Syringes were once marked in cc and clinicians spoke that way, but handwritten cc can be misread as a unit symbol or as a pair of zeros, and medication safety bodies now place it on lists of abbreviations that should not be used. The instruction is to write mL instead, even though the quantity is identical.
Materials science keeps the unit for density. Grams per cubic centimetre is the standard way to state how heavy a substance is for its size: water is 1.00, aluminium 2.70, steel about 7.85, lead 11.34 and gold 19.3. Those numbers are memorable precisely because the cubic centimetre is small enough that everyday solids land between one and twenty.
Modelling and manufacturing use it for part volume. Computer-aided design reports the volume of a component in cubic centimetres, which converts directly to mass once a density is chosen and to material cost in additive manufacturing. It is the natural unit for anything that fits in a hand.
One cubic centimetre equals 1 millilitre, 1000 cubic millimetres, 0.000001 cubic metres, or about 0.061 cubic inches.