This information is from the following soap making book: Beginner Soap Making: Simple Homemade Recipes. I have added it here so that you can get a larger view of the charts if you need to. If you have any questions please contact us.
These numbers are the saponification values in terms of milligrams of potassium (KOH) or sodium hydroxide ( NaOH) required to saponify 1 gram of the given oil.
To convert the SAP values to ounces, do the following:
- For solid soap, divide the SAP value by 1422.9803
- For liquid soap, divide the SAP value by 1010.316
This can be a bit confusing, so here’s an example. If you make a solid soap with just 16 ounces of almond butter as a fat, you would calculate the lye necessary like this:
16 *0.098 = 1.568
16 is the ounces of almond butter you will use, 0.098 is the corresponding lye number from the NaOH column (use this one to make solid soap) and the result is the number of ounces of lye you need.
If you wanted to make a liquid soap with just 16 ounces of aloe vera butter, you would multiply 16 (the number of ounces of fat you are using) by 0.247 (the corresponding caustic soda number) and get 3.952 ounces of caustic soda required to make this soap.
Now, what if you want to use more than one fat to make your soap? You would do the calculations separately and add the amounts of lye together to get the total lye needed. For example:
If you want to make a solid soap with 10 ounces of Acai Berry oil and 15 ounces of Almond Butter, you would do the following calculations:
10*0.136 = 1.36
15 * 0.098 = 1.47
You add 1.36 and 1.47 and get a total lye amount of 2.83 ounces.
So far, so good, right? If not, do not proceed until you understand what you are doing. At best you’ll wind up with soap that doesn’t saponify because you didn’t add enough lye or caustic soda, and at worst you’ll wind up with a soap with too many harsh chemicals in it and will burn your skin.
Also, if you are intimidated by all this, you can run your soap recipe through a lye calculator like the one found at https://www.thesage.com/calcs/lyecalc2.php
When considering conversion from metric to english measures, I don’t understand why the factor of multiplication for saponification values is not exactly 1000 for KOH.
If the definition for SAP value is truly a ratio, then it is unitless, and applies the same ratio across all measurement systems.
E.g., assuming a SAP value of 200 for some oil type, that means 200mg KOH/ 1g oil.
Make similar units makes this .2g KOH/ 1g oil. The ratio of caustic soda to oil is .2 to 1. This would hold true no matter the amount of measure, or what units you used to measure it.
If there’s something I’m missing I would like to know what it is. Thank you.
Newton
how do you calculate the lye and water if you are making a fruit soap using the puree. e.g. avocado and fresh basil soap or papaya soap. thanks.