Find the densities of all involved liquids. These do not need to be derived and can be found by looking in a chemistry book. They are measured in grams per milliliter.
Find the mass of each liquid in the solution. This can be done by weighing the liquids before mixing them or by measuring the total weight after combining individual liquids. Both measuring methods will provide the same results, but measuring the total after each individual addition of liquid is a faster approach. Depending on the degree of accuracy needed, a three-beam or digital scale can be used. Most digital scales do not allow for as precise of a measurement as a three-beam scales.
Calculate the volume of each liquid by dividing mass by the density.
Add the volumes of each liquid. This sum will give you the total volume.