The first step is to determine the amount of liquid the mold holds by filling a round mold with water and then pouring that amount into a measuring cup. Each soap cube equals 1oz. And each mold that I used contained 1/4 cup of liquid. 1/4c equals two fluid ounces. So two cubes melted equals 1/4 cup.
Next, cut the number of glycerine cubes needed and place into a microwave safe measuring cup. Microwave at 30 seconds, stir and then microwave at additional 10 second increments until soap is melted. Stir again.