| Reference | Pints (pt) | Cubic millimeters (mm³) |
|---|---|---|
| A teaspoon | 0.00879877 pt | 5000 mm³ |
| A can of soft drink | 0.580719 pt | 330000 mm³ |
| A wine bottle | 1.31982 pt | 750000 mm³ |
| A bathtub | 263.963 pt | 150000000 mm³ |
| An Olympic swimming pool | 4399385 pt | 2.5 × 1012 mm³ |
The pint in the imperial system is a unit of volume equal to exactly 568.26125 millilitres. Its symbol is pt. It is twenty imperial fluid ounces, an eighth of an imperial gallon, and half an imperial quart. It is the only imperial unit that most people in Britain and Ireland still use every week, and it survives because it is the legal measure for draught beer.
That legal status is precise. Draught beer and cider in the United Kingdom may be sold only in third-pints, half-pints and multiples of half a pint, and the glass itself must carry a verification mark certifying that it holds the stated measure. Publicans can be prosecuted for short measure, so the pint is one of the few units in daily life whose accuracy is actively policed.
Milk keeps the second foothold. Milk sold in returnable glass bottles may still be measured in pints, which is why doorstep deliveries are ordered by the pint while supermarket cartons carry litres. That split is a useful illustration of how metrication proceeded in Britain: it changed the shops and left the traditions alone.
The American pint is a different quantity and the difference is large. A United States liquid pint is 473 millilitres against the imperial 568, so a British pint is about a fifth bigger, and a traveller who orders a pint in New York receives noticeably less than one in Dublin. The American mnemonic that a pint's a pound the world around works only for the American pint; a British pint of water weighs a pound and a quarter.
That weight relationship was once the definition. The imperial system was built so that a gallon of water weighed ten pounds, which makes a pint weigh exactly a pound and a quarter, and the older British rhyme says so directly. Since 1985 the pint has been defined from the metric gallon instead, but the relationship still holds closely enough to be a useful check.
Below the pint the imperial chain runs to the gill at a quarter of a pint and the fluid ounce at a twentieth. Above it come the quart and the gallon. None of these steps is decimal, which is the reason the pint is now the only survivor: it is the one member of the chain that people handle directly, and the rest of the arithmetic has quietly moved to litres.
One imperial pint equals 568.26125 millilitres, 20 imperial fluid ounces, 0.125 imperial gallons, or about 1.201 US liquid pints.
The cubic millimetre is a unit of volume equal to one thousandth of a cubic centimetre, written mm³. It is the volume of a cube one millimetre on each side, and it is exactly one microlitre. Which of the two names is used depends on whether the thing being measured is a solid or a liquid, and the distinction is entirely a matter of professional habit.
Machining measures productivity in it. The material removal rate of a milling cutter or a grinding wheel is quoted in cubic millimetres per minute, and that single figure captures what a machine and a tool can achieve better than spindle speed or feed rate can on their own. Comparing two cutting strategies, two tool coatings or two machines means comparing how many cubic millimetres of metal each turns into swarf per unit time.
Additive manufacturing inverts the same measurement. A fused-filament printer deposits ten to twenty cubic millimetres a second, a laser powder-bed machine rather less, and build time follows directly from the part volume divided by that rate. Because the volume of a component is known exactly from its model, the estimate is unusually reliable.
Wear and durability testing uses the unit to describe loss. A specific wear rate is stated in cubic millimetres removed per newton of load and metre of sliding, which allows materials of very different hardness to be compared on one scale. Bearing life, brake pad testing and coating evaluation all reduce to counting cubic millimetres that are no longer there.
Medical imaging works at the same magnitude. Micro-computed tomography of bone reports trabecular volume and porosity in cubic millimetres, tumour volumes in early imaging are given the same way, and voxel sizes in high-resolution scans are quoted as fractions of one. In each case the unit is small enough to describe structure rather than merely size.
Its identity with the microlitre is worth remembering when moving between fields. An engineer discussing a cubic millimetre of material and a biologist discussing a microlitre of solution are talking about the same quantity, and any calculation that mixes the two needs no conversion factor at all.
One cubic millimetre equals 1 microlitre, 0.001 cubic centimetres, 0.000000001 cubic metres, or about 0.000061 cubic inches.