SoapLab guide
SAP values explained
SAP value soap math is how hobby and professional makers translate grams of oil into grams of alkali. This guide covers what is SAP value in soap making, how to calculate lye using SAP values, how a NaOH table fits oil saponification, and where lye calculation actually happens on SoapLab.
What is SAP value in soap making?
What is SAP value in soap making in plain language: a SAP (saponification) value tells you how much alkali is needed to saponify a unit of fat—when you specify which alkali table you mean. In bar-soap communities, “SAP” often implies a NaOH factor unless the recipe explicitly uses potassium hydroxide (KOH) for liquid soap or dual-lye work.
Different references publish slightly different numbers for the same oil name—supplier, crop year, and measurement method all matter—so treat any NaOH table as versioned: pick one source per recipe line and stay consistent.
Oil saponification: what SAP is measuring
Oil saponification is the reaction between fatty acids from your oils and hydroxide from your lye. SAP values are a practical compression of that chemistry into numbers you can multiply by oil weight—without doing full stoichiometry by hand every batch. They do not replace careful weighing; they organize the arithmetic.
If you need alkali intuition before numbers, read What is lye in soap?
How to calculate lye using SAP values
A common handmade workflow for how to calculate lye using SAP values:
- Weigh each oil (grams).
- For each oil, multiply grams × (NaOH SAP for that oil), using the same units your table expects.
- Sum the contributions for all oils in the blend.
- Apply superfat by reducing the total alkali according to your chosen method—without double-counting superfat in two places.
You can sanity-check intermediate lines with the SAP value calculator, but most full batch sheets are built in the soap calculator, which is designed for multi-oil lye calculation with superfat and water lines.
NaOH table vs KOH: do not mix columns
A NaOH table is not interchangeable with a KOH table by simple substitution. Liquid-soap and dual-lye workflows need the correct alkali type and often different calculators—start from the lye calculator or liquid soap calculator when your recipe language is not NaOH-bar-soap.
Lye calculation habits that prevent disasters
Good lye calculation discipline: one SAP source, one calculator pass you trust, a batch card that records oil lots, and notes when you change suppliers. If oils change, SAP-based alkali changes—treat reformulation as normal, not embarrassing.
For blend thinking before you lock grams, see Soap recipe formulation.
What to do next on SoapLab
Run a recipe in the soap calculator, cross-check unfamiliar oils with the SAP value calculator, and browse the guides index.
Frequently asked questions
Is SAP the same for every book and website?
No—small differences are common. Consistency within one project matters more than debating the third decimal online.
Do I need to memorize SAP values?
You need a reliable table and a repeatable calculator workflow—not memorization.
What is sap value soap makers care about most?
Turning accurate oil grams into accurate alkali grams—because that is what keeps saponification aligned with the recipe you intended.
Where does superfat enter SAP-based lye calculation?
After you compute total alkali from SAP lines—superfat reduces how much hydroxide you use, by the method your tool documents; avoid applying it twice.