| Cubic millimeters (mm³) | Gigaliters (GL) |
|---|---|
| 1 Cubic millimeter | 1 × 10-15 GL |
| 2 Cubic millimeters | 2 × 10-15 GL |
| 3 Cubic millimeters | 3 × 10-15 GL |
| 4 Cubic millimeters | 4 × 10-15 GL |
| 5 Cubic millimeters | 5 × 10-15 GL |
| 10 Cubic millimeters | 1 × 10-14 GL |
| 20 Cubic millimeters | 2 × 10-14 GL |
| 25 Cubic millimeters | 2.5 × 10-14 GL |
| 50 Cubic millimeters | 5 × 10-14 GL |
| 100 Cubic millimeters | 1 × 10-13 GL |
| Reference | Cubic millimeters (mm³) | Gigaliters (GL) |
|---|---|---|
| A teaspoon | 5000 mm³ | 5 × 10-12 GL |
| A can of soft drink | 330000 mm³ | 3.3 × 10-10 GL |
| A wine bottle | 750000 mm³ | 7.5 × 10-10 GL |
| A bathtub | 150000000 mm³ | 0.00000015 GL |
| An Olympic swimming pool | 2.5 × 1012 mm³ | 0.0025 GL |
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.
The gigalitre is a unit of volume equal to a billion litres, or one million cubic metres. Its symbol is GL. It is also exactly one cubic hectometre, which is the same quantity written in coherent SI form. It is the unit in which reservoirs, catchments and national water plans are counted, and it is where water measurement stops describing supply and starts describing landscape.
Dam storage is its principal use. Australian reservoir levels are published in gigalitres and as a percentage of a stated capacity in the same unit, so a city's water security can be read as a single number that changes week by week. Warragamba Dam, which supplies most of Sydney, holds a little over two thousand gigalitres when full, and the whole system a few hundred more.
Policy is written in it as well. The Murray-Darling Basin Plan set out to recover water for the environment in gigalitres, and every argument about that plan has been an argument about how many gigalitres should come out of irrigation and go back into rivers. Desalination plants are rated the same way: a large plant produces something like ninety gigalitres a year, which is a meaningful fraction of a city's demand.
Australians have an informal comparison for it. The volume of Sydney Harbour is taken as roughly five hundred gigalitres, and flood volumes, storage losses and river flows are described in harbours as casually as elsewhere they are described in swimming pools. Two thousand Olympic pools make one gigalitre, which is the more portable comparison for readers elsewhere.
The unit's identity with the cubic hectometre is worth holding on to. Spanish and Latin American hydrology publishes reservoir capacity in cubic hectometres, so a Spanish figure of 500 hm³ and an Australian figure of 500 GL describe exactly the same body of water, and any comparison between the two systems needs no arithmetic at all.
Above the gigalitre, water quantities pass to the cubic kilometre, which is a thousand of them, and are used for lakes, ice sheets and global budgets rather than for anything a government can manage. Below it, the megalitre takes over for individual farms, works and pipelines.
One gigalitre equals 1,000,000,000 litres, 1,000,000 cubic metres, 1 cubic hectometre, or about 264 million US gallons.