# Volume percent

Ethanol volume percent = 40.

Volume percent is a common expression of a solution's concentration. It is the volume fraction expressed with a denominator of 100, and thus is defined as:

$\textrm{volume\ percent} = \frac{\textrm{volume\ of\ solute}}{\textrm{volume\ of\ solution}}*100$

Volume percent is usually used when the solution is made by mixing two fluids, such as liquids or gases. However, percentages are only additive for ideal gases.[1]

The percentage by volume (vol%) is one way of expressing the composition of a mixture with a dimensionless quantity; mass fraction (percentage by weight, wt%) and mole fraction (percentage by moles, mol%) are others.

In the case of a mixture of ethanol and water, which are miscible in all proportions, the designation of solvent and solute is arbitrary. The volume of such a mixture is slightly less than the sum of the volumes of the components. Thus, by the above definition, the term "40% alcohol by volume" refers to a mixture of 40 volume units of ethanol with enough water to make a final volume of 100 units, rather than a mixture of 40 units of ethanol with 60 units of water.