| Milliliters (mL) | Megaliters (ML) |
|---|---|
| 1 Milliliter | 0.000000001 ML |
| 2 Milliliters | 0.000000002 ML |
| 3 Milliliters | 0.000000003 ML |
| 4 Milliliters | 0.000000004 ML |
| 5 Milliliters | 0.000000005 ML |
| 10 Milliliters | 0.00000001 ML |
| 20 Milliliters | 0.00000002 ML |
| 25 Milliliters | 0.000000025 ML |
| 50 Milliliters | 0.00000005 ML |
| 100 Milliliters | 0.0000001 ML |
| Reference | Milliliters (mL) | Megaliters (ML) |
|---|---|---|
| A teaspoon | 5 mL | 0.000000005 ML |
| A can of soft drink | 330 mL | 0.00000033 ML |
| A wine bottle | 750 mL | 0.00000075 ML |
| A bathtub | 150000 mL | 0.00015 ML |
| An Olympic swimming pool | 2.5 × 109 mL | 2.5 ML |
The millilitre is a unit of volume equal to one thousandth of a litre, written mL or ml. It is exactly one cubic centimetre. It is the working unit of medicine, cookery, cosmetics and the laboratory, and it is the smallest volume most people handle deliberately in the course of a day.
Medicine relies on it more heavily than on any other unit of volume. Oral liquids are dosed in millilitres, syringes are graduated in them, intravenous fluids are prescribed as so many millilitres per hour, and blood test results are reported per millilitre or per decilitre. The precision matters: a tenfold dosing error in a paediatric prescription is a difference of a single decimal place in this unit.
That is why the household spoon has been driven out of medical instructions. A teaspoon is nominally five millilitres, but real spoons vary from two to nine, so dosing devices are now supplied with liquid medicines and marked in millilitres. Regulators in several countries require the millilitre marking precisely because it removes an ambiguity that spoons cannot.
Cooking outside the United States runs on it. European and Asian recipes give liquids in millilitres and litres rather than in cups, which is more precise because a cup measures volume by an unstandardised container while a millilitre does not. Wine and spirit measures, coffee shot sizes, and the capacity of a baby bottle are all specified in millilitres.
A convenient identity helps in the kitchen and the laboratory alike. One millilitre of water has a mass of one gram, so a recipe or a protocol can move between mass and volume for water-like liquids without a real error. Cosmetics use the same unit throughout, from a five-millilitre sample to a five-hundred-millilitre bottle.
Against United States and imperial measures it converts awkwardly, and the two differ from each other. One millilitre is 0.0338 United States fluid ounces but 0.0352 imperial fluid ounces, so a fluid ounce is about four per cent larger in Britain than in America, and any drink or medicine volume converted between them needs to state which system was meant.
One millilitre equals 1 cubic centimetre, 0.001 litres, about 0.0338 US fluid ounces, or about 0.0352 imperial fluid ounces.
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.