| Milliliters (mL) | US Gallons (gal US) |
|---|---|
| 1 Milliliter | 0.000264172052358 gal US |
| 2 Milliliters | 0.000528344104716 gal US |
| 3 Milliliters | 0.000792516157074 gal US |
| 4 Milliliters | 0.00105668820943 gal US |
| 5 Milliliters | 0.00132086026179 gal US |
| 10 Milliliters | 0.00264172052358 gal US |
| 20 Milliliters | 0.00528344104716 gal US |
| 25 Milliliters | 0.00660430130895 gal US |
| 50 Milliliters | 0.0132086026179 gal US |
| 100 Milliliters | 0.0264172052358 gal US |
| Reference | Milliliters (mL) | US Gallons (gal US) |
|---|---|---|
| A teaspoon | 5 mL | 0.00132086 gal US |
| A can of soft drink | 330 mL | 0.0871768 gal US |
| A wine bottle | 750 mL | 0.198129 gal US |
| A bathtub | 150000 mL | 39.6258 gal US |
| An Olympic swimming pool | 2.5 × 109 mL | 660430 gal US |
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 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.