Is a Lye Calculator Necessary?


Using lye to make soap is a necessity. Without lye there is no saponification process and therefore no soap. How do you know how much lye to use? You use a Lye Calculator.

Yes, a lye calculator is a necessary safety tool every soap maker should use. It calculates the correct amount of lye for each soap batch with accuracy and dependability. You should always use a lye calculator to check every recipe.

Why is it Important to Use a Lye Calculator?

• Safety is the number 1 reason to use a lye calculator.

• Accuracy is the number 2 reason to use a lye calculator.

• Every oil (or fat) available for soap making has its own amount of lye needed for turning into soap

• When you are combining different oils in the same recipe, the amount of lye will be different for each oil.

• While these calculations can be done by hand, using a calculator removes the likelihood of errors in math.

• The amount of oils, as well as the type of oils being used will impact the amount of lye a recipe will need.

• Even small changes in the measurements or type of oil can have major changes on the outcome of the recipe.

• It saves time. I was always good at math, but the time it would take to do these calculations by hand (without error) would take me quite a significant part of my morning.

• It allows you to make changes on the fly. What I mean by this is if you are planning a recipe and you go to grab your Jojoba oil, and you realize you are out, you can quickly edit the recipe in the calculator. You can substitute another oil in its place and immediately get the adjusted Lye calculation. In my mind, this is an absolute treasure in its own right.

Which Lye Calculator do I Use?

I personally use The Sage Lye Calculator and find it easy to use, understand and extremely dependable. Some of the specific things I like about this particular calculator are:

1. The super fat % and the corresponding lye amount.

2. The list of oils is very good

3. It allows for different liquids for mixing with the lye

4. It allows for calculations of Lye as well as Potassium Hydroxide

5. It provides a recipe sheet with basic instructions

6. I can name and save each recipe I design

7. It has a place for notes about the recipe.

8. They also have a Fragrance Oil Calculator on their site that is very useful and helpful.

What is a Lye Calculator?

A lye calculator is a calculator that allows the soap maker to enter the exact amount of each specific ingredients of a soap recipe into a form. It will ask you the unit of measurement you are using, the liquid you are using, and the type of hydroxide you are using (either Sodium or Potassium) and then it calculates the correct amount of lye or potassium hydroxide you will need as well as the recommended amount of liquid to dissolve it into.

This is a very complicated computation which I prefer to use a calculator for myself. Many calculators allow you to choose if you are using Sodium Hydroxide, Potassium Hydroxide, Lye water percentages, or a combination of both. They also allow you to change the liquid you will be using, for example water, tea, milk, or combinations.

Most lye calculators allow you to enter ounces, grams, or percentages which are the most common forms of measurement in soap making. All measurements for soap making are done by weight not volume. This is important to remember. The only exception to this is your water.

What Are SAP Values?

SAP values refer to the specific and individual saponification number for any fat or oil. Each oil has its own SAP value. It refers to the number of milligrams of potassium hydroxide or sodium hydroxide each oil needs to convert the fat into soap. The SAP value for each oil will have 2 numbers, one for Sodium Hydroxide (Lye) and a different number for Potassium Hydroxide. For example, Sweet Almond Oil has an SAP Value of .137 for Sodium Hydroxide and .194 for Potassium Hydroxide. Very different numbers if you are calculating things yourself.

Not All Oils Are Created Equal

Each oil brings to the recipe a different benefit to the skin, to the soap, to the mechanics of the soap making process itself. Some different oil benefits that vary by the type of oil include:

• Cleans the skin

• Moisturizes the skin

• Tightens the skin

• Helps attract and hold moisture in the skin

• Great for the skin in general

• Great for bubbles and makes a lot of big bubbles

• Makes lasting bubbles that lather really well

• Hardens the soap bar making it last longer

• Slows trace so you can work with the soap to add color, scents, designs

• Accelerates trace which means you need to work quicker with the wet soap.

• Gentle on the skin (which makes them ideal for sensitive skin)

• They contain vitamins and valuable minerals for the skin

What Oils Do What?

With all of the different oils available to the soap maker, you can choose the ones that meet your needs in your soap. This variety is one of the most important reasons for the NEED to use a lye calculator. Each oil does something different, and each oil has a different saponification value. With the infinite number of possible combinations that you can invent, it is imperative that your lye calculations be correct. This can not be said often enough.

Using a lye calculator will help you make better soap, easily adjust your recipes, and can save you from horrible messes and wasted costly oils when the recipe is not right. Another benefit is that it provides you with a recipe sheet that shows the complete recipe with each oil listed, both in ounces, or grams and percentages, the lye amount for each super fat % and the range for your water. This is helpful because you can write it down on an index card, and keep it with each batch you make.

A Chart to Show the Difference

Here is short chart showing just a few oils used in soap making and their characteristics. Please notice the differences in the SAP values for each of them. It is important to note, that these values are for Sodium Hydroxide (LYE) and not Potassium Hydroxide. It takes more Potassium hydroxide to saponify the same amount of fat than it does sodium hydroxide (lye). Potassium Hydroxide is used when making liquid soap not bar soap.

These are just a few oils that can be used in soap making and other skin care products. The variety in the kinds of oils, fats, butters and other ingredients available to the soap maker is vast. The SAP values for each of these ingredients is unique to each ingredient, and must be calculated in proportion to the amount of each oil used in the recipe. My head gets dizzy just thinking about doing the math.

To Sum It Up

Literally, “to sum it up” is exactly why a lye calculator is necessary. There are so many calculations, figures, percentages and variables to add together for each recipe, a lye calculator just makes sense. It is safe, dependable, saves time, saves making mistakes (hence saves money) , saves your sanity, and allows you to spend your time enjoying the creative fun of your craft instead of spending more time doing math than making soap. I wouldn’t soap without one.

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