mL
A milliliter (ml or mL) is a metric unit of volume. It is based on the liter (L), and uses the the prefix "milli-", which is one of a set of prefixes used in the International System of Units (SI) to indicate that it is 
L. In terms of cubic meters, the base unit of volume in SI:
1 mL = 0.000001 m3
1 m3 = 1,000,000 mL
A milliliter is exactly equal to a cubic centimeter (cm3), which is another SI derived unit of volume. 1 cubic centimeter (and therefore 1 mL) is equal to the volume of a cube with edges that measure 1 cm each:
A volume in milliliters can therefore be visualized as the space occupied by some number of the cubes above. For example, a volume of 16 mL could be represented using 16 cubes, each with a volume of 1 cm3:
Units of volume
As mentioned, a liter is not an SI unit, but it is accepted for use with SI. As a unit that is accepted for use in SI, SI prefixes such as "milli-" (10-3) can be applied to the unit of liters. This is beneficial because SI prefixes make it easy to express larger or smaller measurements as multiples or submultiples of a base unit (in this case the liter) that are all related by powers of 10. Milliliters and liters are the most commonly used, but centiliters (10-2), deciliters (10-1), kiloliters (103), and any other prefixed form of the liter can be used to best suit the magnitude of whatever is being measured.
In contrast, units of volume in the US customary system do not use prefixes. They all have specific relationships that are not based on powers of 10, so to convert between units of volume in the US customary system, it is necessary to know (or be able to reference) the various conversion factors between units. Below are some common units of volume in the US customary system and how they relate to milliliters.
| 1 mL | = 1 cm3 |
| 1,000 mL | = 1 L |
| 1,000,000 mL | = 1 m3 |
| 28,316.847 mL | = 1 ft3 |
| 3,785.411 mL | = 1 gallon |
| 240 mL | = 1 cup |
Example
Jenny's family drinks 4 gallons of milk a month. How many milliliters of milk do they drink?
There are 3,785.411 mL in 1 gal, so multiply 3,785.411 by 4:
3,785.411 × 4 = 15,141.644 mL
Jenny's family drinks 15,141.644 mL (or 15.142 L) of milk in 1 month.
Milliliters vs cubic centimeters
As mentioned above, milliliters and cubic centimeters are equivalent measurements. They represent the same exact volume, meaning that 10 mL = 10 cm3. They are both SI derived units of volume, but milliliters are used more frequently than cubic centimeters.
In some cases, the distinction between when to use cubic centimeters or milliliters is made based on whether or not the volume being measured is a solid; solid objects are measured using cubic centimeters while liquids (or gases) are measured using milliliters. However, this distinction is only sometimes made, and it is not incorrect to use either measurement regardless of the state of the object being measured.
Further confusion may arise when comparing milliliters, cubic centimeters, and grams. In the past, the gram was defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre, and at the temperature of melting ice." Based on this definition, milliliters, cubic centimeters, and grams were all equivalent given the specific conditions stated above. However, since mass is affected by temperature and pressure, in most everyday cases, 1 gram of water will likely be close, but not exactly equal 1 cm3 or 1 mL.