SAP value

The SAP value, short for saponification value, is a number that tells you how many milligrams of lye are needed to saponify one gram of a particular fat or oil. Every oil has its own SAP value because each one is made of a different mix of fatty acids, and the value differs depending on whether the lye is sodium hydroxide or potassium hydroxide.

SAP values are what make lye calculators possible. When you enter your oils and their weights into a calculator, it multiplies each oil's SAP value by its weight to find the total lye needed, then applies your chosen superfat percentage on top. Without this number, there is no reliable way to know how much lye a recipe actually calls for.

When looking up SAP values, use a current, reputable chart or calculator database rather than an old printout, since exotic or blended oils are sometimes missing or listed inconsistently across sources. A frequent mistake is mixing up the sodium hydroxide and potassium hydroxide SAP values for the same oil, which produces a recipe with the wrong amount of lye for the type of soap being made.