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Free soap making tool
Lye calculator (NaOH)
Sodium hydroxide and water for your oils, with superfat and lye concentration. Always double-check before you weigh lye.
Weigh out
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Water–
Oils–
Water : lye–
Batch–
Lye is caustic: gloves, goggles, ventilation, and always add lye to water, never water to lye.
Questions
How is the lye amount calculated?
Lye = Σ (oil grams × SAP value) × (1 − superfat) ÷ purity. SAP values are in grams of KOH per gram of oil and are converted to NaOH by molar mass (39.997 / 56.106).
What superfat should I use?
5 % is a common starting point for bar soap: a little oil stays unsaponified for a milder bar. Salt bars and 100 % coconut soaps often use 15–20 %.
Where do the SAP values come from?
From the SoapCalc oil list, cross-checked against published saponification values. Oils from different suppliers vary, so treat results as a starting point.