| Teraliters (TL) | Decaliters (daL) |
|---|---|
| 1 Teraliter | 100000000000 daL |
| 2 Teraliters | 200000000000 daL |
| 3 Teraliters | 300000000000 daL |
| 4 Teraliters | 400000000000 daL |
| 5 Teraliters | 500000000000 daL |
| 10 Teraliters | 1000000000000 daL |
| 20 Teraliters | 2000000000000 daL |
| 25 Teraliters | 2500000000000 daL |
| 50 Teraliters | 5000000000000 daL |
| 100 Teraliters | 10000000000000 daL |
| Reference | Teraliters (TL) | Decaliters (daL) |
|---|---|---|
| A teaspoon | 5 × 10-15 TL | 0.0005 daL |
| A can of soft drink | 3.3 × 10-13 TL | 0.033 daL |
| A wine bottle | 7.5 × 10-13 TL | 0.075 daL |
| A bathtub | 1.5 × 10-10 TL | 15 daL |
| An Olympic swimming pool | 0.0000025 TL | 250000 daL |
The teralitre is a unit of volume equal to a thousand gigalitres, or 1,000,000,000,000 litres. Its symbol is TL. It is exactly one cubic kilometre, and that is how the quantity is almost always written, because at this scale what is being measured is no longer a container but a piece of the planet.
Lakes are the obvious application. Lake Baikal holds about 23,600 cubic kilometres of fresh water, more than any other lake on earth, and Lake Superior about 12,100. Those two figures alone amount to a fifth of the world's unfrozen surface fresh water, which is the kind of statement the unit exists to make.
Rivers are described by the volume they move rather than by what they hold. The Amazon discharges roughly 6600 cubic kilometres a year into the Atlantic, more than the next several rivers combined, and total human withdrawal of fresh water from all sources runs to about 4000 cubic kilometres a year. Setting those two numbers side by side in the same unit is one of the clearest ways to state the scale of water use.
Ice is measured here too, and the numbers are larger again. The Greenland ice sheet contains close to 2.9 million cubic kilometres, and in recent decades it has been losing a few hundred each year, a figure that converts directly into millimetres of sea level because the ocean's surface area is known. The Antarctic sheet is an order of magnitude larger still.
The ocean itself sets the ceiling. All the seawater on earth amounts to about 1.335 billion cubic kilometres, so a single teralitre is roughly one billionth of it. Below the ocean, the largest managed water bodies are engineered reservoirs, and even the biggest of those hold only a few tens of cubic kilometres.
In practice the name teralitre is rare and the cubic kilometre is standard. Hydrology, glaciology and climate science all use km³, and a figure given in teralitres is more likely to come from a water utility extending its own gigalitre scale upward than from a scientific source. The two are identical, so no conversion is needed, only recognition.
One teralitre equals 1,000,000,000,000 litres, 1,000,000,000 cubic metres, 1 cubic kilometre, or 1000 gigalitres.
The decalitre is a unit of volume equal to ten litres. Its symbol is daL, and the spelling dekalitre is also accepted. It sits between the litre of the household and the hectolitre of the trade, and although it once had a settled place in European markets it is now among the least written of the metric volume units.
Its historical role was as a physical measure rather than a number. Nineteenth-century French markets sold grain, potatoes, chestnuts and dried beans out of stamped cylindrical vessels holding one decalitre, half a decalitre or a double one, and a trader's set of these was inspected and verified like a set of weights. Selling dry goods by volume was faster than weighing them and needed no balance, so the vessels did real work.
Weighing displaced it. Once cheap accurate scales became universal, dry goods moved to mass, which is fairer to the buyer because it does not depend on how densely a load happens to settle. The decalitre lost its purpose along with the practice, and the vessels survive in museums and in the vocabulary of a few older markets rather than in commerce.
The quantity itself remains perfectly ordinary. Ten litres is a large household bucket, half a jerrycan, the fuel tank of a scooter, or a fortnight of drinking water for one person. It is roughly the volume of a cubic vessel twenty-two centimetres on a side, and it weighs ten kilograms when filled with water.
What killed the unit as a written form was the same pressure that removed deca everywhere else. Metric practice steps by factors of a thousand, so litres serve until about a thousand of them and hectolitres take over for trade quantities. Ten litres is written 10 L, which is shorter than 1 daL, needs no explanation, and sorts correctly beside 5 L and 200 L in the same table.
When the unit does appear, usually in an old record or a translated document, the conversion is a single step. Multiply by ten for litres, divide by ten for hectolitres, and the resulting figure will match modern usage without any loss of precision.
One decalitre equals 10 litres, 0.1 hectolitres, about 2.64 US gallons, or about 2.2 imperial gallons.