Determine the volume or mass of the solute. Liquids are typically measured in milliliters of volume and solids in grams of mass. Either one may be used in volume percentages in the exact same way.
Determine the total volume of the solution in milliliters.
Divide the volume or mass of the solute by the total volume of the solution and multiply by 100. As an example, say you determined you had 182 ml of isopropyl alcohol in a solution that totaled 200 ml. You would divide 182 by 200, which yields 0.91. You then multiply this by number by 100 to convert to a percentage, giving you 91 percent, which is the higher concentration of rubbing alcohol available to consumers.