# Volume

Volume is the amount of three-dimensional space occupied by an object, substance, or closed surface. For example, think of the space an apple would take up in a bag. The remaining volume of the bag is the amount of space left in the bag after subtracting the volume of the apple.

To conceptualize volume, we can also use the same method as we do with area, except rather than using a square as we do with area, we add an additional dimension, and use a cube.

The cube above can be referred to as a unit cube. The volume of a unit cube can be found by multiplying its length, width, and height (or depth). Each of these measures 1 unit, so:

1 unit × 1 unit × 1 unit = 1 unit^{3}

The volume of a given object can then be measured as the number of unit cubes that make up the object.

## Units of volume

The most commonly used systems of measurement around the world are the International System of Units (SI), the US customary system, and the imperial system of measurement. Almost all countries use SI to some degree, while the US customary system is used in the US and its territories, and the imperial system is used in the UK and its territories. Below are some units of volume in the various systems of measurement.

**International System of Units:**

Liter (L), cubic centimeter (cm^{3}) or milliliter (mL), cubic meter (m^{3}).

**US customary system and imperial system**

Gallon (gal), fluid ounce (fl oz), cup (C), cubic foot (ft^{3}), cubic yard (yd^{3}).