Soap Lye Calculator
Plan lye and water from typical published SAP values. This is a planning tool, not a substitute for independent checks or safety practice.
Safety
Lye is caustic. Wear eye protection and gloves. Add lye to water, never water to lye. Independently verify these amounts against your oil supplier data and another trusted calculator before mixing. This tool is for planning only.
Oils
Lye required
141.27 g NAOH
- Oil weight
- 1,000.00 g
- Water
- 286.82 g
- Lye solution
- 428.09 g
- Superfat
- 5%
SAP values are typical published averages (grams NaOH per gram of oil). KOH uses NaOH × 1.40275. Confirm before use.
Each oil contributes oil grams × SAP (NaOH). KOH uses NaOH SAP × 1.40275 (molecular weight ratio). Superfat reduces lye. Water comes from lye concentration: water = lye × (100 − conc) / conc.
SAP values are typical published averages for planning. They are not your supplier’s certificate of analysis.
How this calculator works
How we calculate this
- Lye before superfat = Σ (oil grams × SAP)
- Lye = that amount × (1 − superfat %)
- Water = lye × (100 − concentration) / concentration
- KOH SAP = NaOH SAP × 1.40275
Example
Example: 1 kg olive oil, 5% superfat, 33% NaOH solution
Olive SAP 0.135 → 135 g NaOH before superfat, 128.25 g after 5% superfat. Water at 33% concentration is about 260 g.
- Changing superfat from 0% to 5% is a real lye reduction.
- Always verify with a second source before mixing.
How much should I charge?
This calculator does not price soap. Use the soap cost calculator after you know batch ingredients.
Pricing tips
- Work in grams.
- Add oils that match your recipe; remove unused rows.
- If your oil COA lists a different SAP, trust the COA.
Common mistakes
- Using this as the only check before a live lye mix.
- Pouring water onto lye (always add lye to water, with proper PPE).
- Mixing up NaOH and KOH.
FAQ
How does this lye calculator work?
It multiplies each oil weight by a typical SAP value, reduces lye by superfat, then calculates water from the concentration you enter.
Are these chemical formulas invented?
No. Saponification values and the KOH/NaOH weight ratio are standard soapmaking relationships. The SAP table is still an average — verify before use.
Related calculators
- Soap Cost Calculator — Price a soap batch and each bar from oils, lye, fragrance, labor and packaging.