# Volume fraction

In chemistry, the volume fraction φj is defined as the volume of a constituent Vj divided by the volume of all constituents of the mixture V prior to mixing:[1]

$\phi_j = \frac {V_j}{\sum_i V_i}$

Being dimensionless, its unit is 1; it is expressed as a number, e.g., 0.18 or 18%.

Volume fraction is also called volume concentration in ideal solutions where the volumes of the constituents are additive (the volume of the solution is equal to the sum of the volumes of its ingredients).

The sum of all volume fractions of a mixture is equal to 1:

$\sum_{i=1}^{N} V_i = V ; \qquad \sum_{i=1}^{N} \phi_i = 1$