What Is A Soap Calculator

The purpose of a soap calculator is to determine how much lye will be required to neutralize an amount of oil or oils, and turn it into soap. This process is called saponification. There are quite a few homemade soap making sites that have soap calculators where all you have to do is plug in the weight of the oils you are using, and the soap calculator then tells you how much lye you need.

I have always found it easier to use a plain old hand held calculator and a saponification table like the one below. Maybe it’s just me, but I tend to trust myself more than an online calculator. A soap calculator doesn’t have to be complicated, which is why I use the table and do the math myself.

The table below gives the multipliers for some of the more popular oils used in homemade soap making and is very easy to use. As you can see, it only has three columns.

The first column is the name of the oil.

The second column, called SAP Value, uses a percentage of lye that yields a basic soap.

The third column, labeled Milder, produces more of a moisturizing soap because it uses a little less lye. This leaves some of the fatty acids from the oils not neutralized, which gives the soap a humectant property, good for moisturizing the skin. Using the numbers in the Milder column eliminates the need for superfatting. Superfatting is the process of adding extra fat to your soap in order to make it a moisturizing soap. Using a little less lye to begin with accomplishes the same purpose.

What You Need To Know About Soap Calculators

The first thing you need to know about using a soap calculator, whichever one you decide to use, is that all your ingredients, except the water, are measured by weight, not by volume. Water is in a class by itself because it is the only substance on Earth that has a density of 1. This simply means that one milliliter (ml) of water weighs one gram or, in the English or Imperial system, one fluid ounce of water weighs one dry measure ounce.

So, leaving all the chemistry mumbo-jumbo behind, if your soap recipe calls for 100 grams of water, you will measure out 100 ml. Using Imperial measure, if your recipe calls for 16 dry measure ounces of water, you will measure out 16 fluid ounces. Simple enough.

The other thing you won’t see in the table is how much water to use. Water’s only purpose in this process is to dissolve the lye, so the standard ratio is two parts water to one part lye. Less water will work, but all lye will have some impurities in it, so it is best to use the 2:1 ratio to make sure all the impurities are also dissolved.

More water will also work, but will lengthen the curing time, since the main purpose of the curing process is to let the water evaporate out of your soap. The curing time at a 2:1 ratio is about four weeks.