Saponification Values: How SAP Values Calculate Soap Lye
Learn how soap calculators use SAP values for each oil, why NaOH and KOH values differ, and why copied lye numbers can be unsafe.
What a SAP value represents
A saponification value describes how much alkali is required to saponify a given amount of fat or oil. Coconut oil, olive oil, shea butter, and every other material have different fatty acid profiles, so they do not use the same amount of lye.
NaOH and KOH SAP values are different
SAP data may be expressed for sodium hydroxide or potassium hydroxide. The values are not interchangeable. A calculator must use the correct basis, apply the weight of each oil, combine the results, and then account for superfat and alkali purity.
Why values can vary slightly
Published SAP values are representative averages because natural oils vary by source and batch. Reputable calculators use established reference data and a deliberate lye discount. Always calculate the exact oil blend rather than copying the lye amount from a recipe with different ingredients.