How do you convert percent weight to percent volume?

Answer 1

This requires knowing the ratio of the density of the specific component versus the density of the full material. In the OP's first response, it would not do to simply multiply the wt% by the density in units of g/ml. The calculation must involve both the subcomponent's density (in the previous example, the benzine) as well as the overall material density (that of the gasoline, which the benzine is a subcomponent of).

Therefore, it is necessary to multiply the wt% by the ratio overall material density: vol% = wt% * (Density of Overall Material)/(Density of Subcomponent) = 2.5wt% * (Density of Gasoline)/Density of benzine

Answer 2

to calculate the weight from the volume, you always multiply by the density. example: If the benzene content is 2.5%v/v, then in 100mL of gasoline, you have 2.5mL of benzene. If the density of Benzene at 15.5°C is 0.81g/mL, then 2.5 x 0.81 = 2.0%w/v.