| Decaliters (daL) | Megaliters (ML) |
|---|---|
| 1 Decaliter | 0.00001 ML |
| 2 Decaliters | 0.00002 ML |
| 3 Decaliters | 0.00003 ML |
| 4 Decaliters | 0.00004 ML |
| 5 Decaliters | 0.00005 ML |
| 10 Decaliters | 0.0001 ML |
| 20 Decaliters | 0.0002 ML |
| 25 Decaliters | 0.00025 ML |
| 50 Decaliters | 0.0005 ML |
| 100 Decaliters | 0.001 ML |
| Reference | Decaliters (daL) | Megaliters (ML) |
|---|---|---|
| A teaspoon | 0.0005 daL | 0.000000005 ML |
| A can of soft drink | 0.033 daL | 0.00000033 ML |
| A wine bottle | 0.075 daL | 0.00000075 ML |
| A bathtub | 15 daL | 0.00015 ML |
| An Olympic swimming pool | 250000 daL | 2.5 ML |
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.
The megalitre is a unit of volume equal to one million litres, or one thousand cubic metres. Its symbol is ML. It is the working unit of water management: irrigation entitlements, treatment works capacity, farm dams and the trading of water rights are all counted in megalitres, because the quantities involved are far too large for litres and awkwardly small for cubic kilometres.
Australia has made the most of it. Irrigation water in the Murray-Darling Basin is held as entitlements measured in megalitres, seasonal allocations are announced as a percentage of those entitlements, and the resulting rights are traded on an open market where prices are quoted in dollars per megalitre. That market is among the largest of its kind in the world, and every price in it is a price per million litres.
British water utilities use it for throughput. A treatment works is rated in megalitres per day, distribution zones are balanced in the same unit, and leakage is reported as megalitres lost daily across a network. Because a large city consumes several hundred megalitres a day, the unit keeps national and regional figures in three or four digits rather than in unreadable strings of zeros.
A familiar object fixes the scale. An Olympic swimming pool of fifty metres by twenty-five, filled to two metres, holds 2500 cubic metres, which is two and a half megalitres. Journalism uses that comparison constantly for reservoir levels and flood volumes, and it works precisely because the pool and the unit are within a factor of three of each other.
On farms the unit describes storage. An Australian farm dam might hold anything from five to fifty megalitres, an on-farm irrigation season is planned in megalitres per hectare, and evaporation losses from open storage are estimated the same way. Sewage treatment, industrial process water and mine site water balances all follow.
Its one hazard is typographic. In the correct symbols, mL is a millilitre and ML is a megalitre, and the two differ by a factor of a thousand million. A document that is careless about capitals can therefore turn a laboratory volume into a reservoir, which is why water and clinical writing both insist on the case being right.
One megalitre equals 1,000,000 litres, 1000 cubic metres, about 264,172 US gallons, or about 220,000 imperial gallons.