Soap calculator: exact NaOH & KOH amounts
Calculate lye, water and superfat for bar soap, liquid soap and dual lye – including the automatically generated INCI list of your finished soap.
Soap calculator
- • Lye into water, never the reverse.
- • Goggles + gloves (no latex).
- • No aluminium – only steel/glass/plastic.
The calculated lye amount is a guide value without warranty – verify SAP values and purity against your raw materials' data sheets (CoA/SDB).
Add oils to calculate the lye amount and INCI list.
This calculator is a free calculation and orientation aid – not a safety assessment, not a safety or sale clearance, and not a checked label. SAP values are batch-dependent averages from public literature; results may differ from your raw material. Check the lye amount, purity and protective equipment before every batch against the data sheets (CoA/SDB). Responsibility for the recipe, safe production and legal compliance (CPSR, PIF, CPNP) lies solely with you.
How saponification works
Every oil has its own saponification value (SAP) – the amount of lye needed to fully turn it into soap. The calculator sums it per oil and accounts for purity and superfat.
Lye + oil yield soap + glycerin. Superfat deliberately leaves some oil unsaponified – as a safety buffer against SAP variation and for skin care.
Choose oils
Enter oils and amounts – with verified SAP values.
Lye & water
NaOH/KOH amount, superfat and water are calculated live.
INCI list
The INCI declaration is generated automatically – as a draft to review and complete.
Handling lye safely
Sodium/potassium hydroxide is strongly corrosive (GHS05, H314) and heats up when dissolved. Please observe:
- Always add the lye slowly to cold water – never the other way around.
- Wear safety goggles and nitrile/neoprene gloves (no latex); ensure ventilation.
- Use only stainless steel, glass, HDPE or silicone – never aluminium (hydrogen formation).
- On skin contact rinse with water for at least 20 minutes – no vinegar. Eyes: go to emergency care immediately.
- Keep children and pets away. Cure the soap for 4–6 weeks.
Oil database with verified SAP values
166 common oils and butters with saponification value and fatty-acid profile – from coconut and olive to shea butter, cocoa butter and castor.
From recipe to a ready INCI list
Unlike plain lye calculators, INCIkit automatically creates your soap's INCI declaration: saponified oils become sodium/potassium salts (e.g. Sodium Cocoate), superfat oils, Aqua and Glycerin included – ordered per EU Regulation 1223/2009 Art. 19.
Note: NaOH/KOH never appear on the label – they are saponified in the finished product.
Frequently asked questions
How do I calculate the NaOH amount for soap?
For each oil the saponification value is multiplied by the oil weight and summed; superfat is subtracted and NaOH purity is taken into account. The calculator does this automatically and rounds the lye amount down for safety.
What is the difference between NaOH and KOH?
NaOH (sodium hydroxide) makes bar soap, KOH (potassium hydroxide) makes liquid soap. KOH is usually only ~90% pure – the calculator corrects for this. Dual lye combines both.
What does superfat mean?
Superfat is the share of oil left unsaponified on purpose – for skin care and as a safety buffer. Typical values are 5–8%.
Does the calculator also create the INCI list?
Yes. From your oils, INCIkit automatically generates the finished soap's INCI declaration, ordered per EU law.
Does the calculator replace the safety assessment?
No. The calculator is a calculation and orientation aid, and the generated INCI list is a draft, not a checked label. Anyone selling soap in the EU is the 'responsible person' under Regulation (EC) 1223/2009 and needs, among other things, a safety assessment (CPSR), a PIF and the CPNP notification – responsibility lies with you.
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From soap recipe to complete production documentation
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