Whether you use a traditional soap mold or some other container, you can calculate just how much soap you need to make to fill that particular mold. Soap Calculators ​There are a number of great online Lye/Soap Calculators to assist you in making sure that your soap batch is going to fit your mold. Click on the links below to check out these calculators to see which is your preferred option. LyeCalc (my favourite and the one I typically use when creating a new recipe) Soap