Volume (also called capacity) is a quantification of how much space an object occupies.

The SI unit of volume is **cubic metre **(American spelling meter) , equal to 1000 liters, 1.307 95 cubic yard, or 35.3147 cubic feet. A cubic meter holds about 219.99 British Imperial gallons or 264.17 U.S. liquid gallons.

Measuring volume isn't always easy because objects have regular or uniform shapes and irregular shapes.

The volume of regular objects can usually be measured with a formula.

The volume of irregular objects is often measured by a system called water displacement. A certain amount of water is placed in a container and the height of the water is marked. The irregular shape object is put into the water, and the irregular object causes the water line to rise.

This new water level is marked. When the irregular object is removed from the water, the water line goes back to its original place. Measuring how much water is needed to meet the raised water line tells you the volume of the irregular object. The difference between the first line and the raised line measures the volume of the object.

A common metric unit of volume is **liter or litre (L or l)**.The liter was originally defined, in 1964, to be the volume occupied by a kilogram of water but,unfortunately, the physical objects constructed to represent the meter and kilogram disagreed slightly.In 1901 at the 3rd CGPM conference the litre was redefined as the space occupied by 1 kg of pure water at the temperature of its maximum density (3.98 °C) under a pressure of 1 atm and formally defined the liter to be

exactly 1.000 028 dm 3 .

No one was particularly happy with such an awkward definition, and in 1964 the CGPM repealed the definition and the litre was once again defined in exact relation to the metre, as another name for the cubic decimetre, that is, exactly 1 dm³.

Compared to the customary volume units, the liter is a little more than a U. S. liquid quart (1.056 688 qt or 33.814 fluid ounces ) but a little less than a U. S. dry quart (0.908 08 qt) or a British imperial quart (0.879 89 qt or 35.195 fluid ounces).

Another common unit is gallon.Gallon is a unit of volume in the U.S. Customary System (3.785 liters) ) and in the British Imperial System (4.54609 liters).