| US Gallons (gal US) | Teraliters (TL) |
|---|---|
| 1 US Gallon | 3.785411784 × 10-12 TL |
| 2 US Gallons | 7.570823568 × 10-12 TL |
| 3 US Gallons | 1.1356235352 × 10-11 TL |
| 4 US Gallons | 1.5141647136 × 10-11 TL |
| 5 US Gallons | 1.892705892 × 10-11 TL |
| 10 US Gallons | 3.785411784 × 10-11 TL |
| 20 US Gallons | 7.570823568 × 10-11 TL |
| 25 US Gallons | 9.46352946 × 10-11 TL |
| 50 US Gallons | 1.892705892 × 10-10 TL |
| 100 US Gallons | 3.785411784 × 10-10 TL |
| Reference | US Gallons (gal US) | Teraliters (TL) |
|---|---|---|
| A teaspoon | 0.00132086 gal US | 5 × 10-15 TL |
| A can of soft drink | 0.0871768 gal US | 3.3 × 10-13 TL |
| A wine bottle | 0.198129 gal US | 7.5 × 10-13 TL |
| A bathtub | 39.6258 gal US | 1.5 × 10-10 TL |
| An Olympic swimming pool | 660430 gal US | 0.0000025 TL |
The United States gallon is a unit of volume equal to exactly 231 cubic inches, or 3.785411784 litres. Its symbol is gal US. It contains four quarts, eight liquid pints and 128 United States fluid ounces, and it is about a fifth smaller than the imperial gallon still used in Britain and Ireland.
It is older than its British rival. The figure of 231 cubic inches comes from the English wine gallon standardised in 1707 under Queen Anne, which was the common measure across the American colonies. When Britain abolished its several gallons in 1824 and replaced them with a single imperial gallon based on ten pounds of water, the United States simply kept the one it already had, and the two systems have diverged ever since.
Fuel makes it the most politically visible unit in American life. The price of a gallon of gasoline is quoted daily, watched by governments and used as shorthand for the cost of living, and vehicle efficiency is stated in miles per gallon on every window sticker. Because the American gallon is smaller, a car rated at 30 miles per gallon in the United States would be described as 36 in Britain, which is the same car and the same fuel.
The petroleum industry counts in a multiple of it. The barrel of crude oil is defined as 42 United States gallons, a figure fixed in the Pennsylvania oil fields in the 1860s when a 40-gallon barrel plus two gallons of allowance for leakage became the trade standard. Every published figure for world oil production and reserves rests on that convention.
Domestic quantities follow the same measure. Milk, paint, water for the garden, propane and swimming pool chemistry are all sold and dosed by the gallon in the United States, and a gallon of fresh water weighs 8.34 pounds against the imperial gallon's ten. That difference in weight is a useful check when a figure of uncertain origin needs to be identified.
Care with labelling matters when the two gallons meet. A liquid described simply as a gallon in an American document is 3.785 litres and in a British one 4.546, and nothing in the word itself distinguishes them. Writing gal US or specifying litres removes an ambiguity that has caused real errors in shipping, aviation and chemical dosing.
One United States gallon equals 3.785411784 litres, 231 cubic inches, 128 US fluid ounces, or about 0.833 imperial gallons.
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.