Soap Calculator
Calculate the precise amount of lye (sodium hydroxide) and water needed for cold process soap making based on your oils and desired superfat percentage.
Published by:
isCalculator Editorial Team
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How to Use the Soap Calculator
This calculator helps you determine the correct amount of lye (NaOH) and water for cold process soap making. All measurements are in ounces (oz).
Step-by-Step Instructions
- Enter oil amounts in the five oil fields (Oil 1 through Oil 5). Use only ounces (oz). You can leave unused fields at 0.
- Set your superfat percentage (default is 5%). This is the percentage of oils that will remain unsaponified. Range: 0–30%.
- Click the "Calculate" button.
- View the results below the button:
- Total Oil Weight – sum of all oils entered.
- Lye (NaOH) Needed – adjusted for your superfat.
- Water Needed – calculated as 38% of total oil weight.
Important Notes
- All inputs must be in ounces (imperial). Do not use grams or milliliters.
- If you see an error, check that at least one oil is greater than 0 and superfat is between 0 and 30.
- The calculator uses standard SAP values for common oils. Adjustments for specific oils are not supported.
Formula: Lye = Σ(oil weight × SAP value) × (1 - superfat%). Water = 38% of total oil weight.
Previous Results
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Frequently Asked Questions
Superfat is the percentage of oils that remain unsaponified in the soap, providing moisturizing properties. Typical range is 5-8%.
Too much lye can cause skin irritation, while too little can result in a soft soap that doesn't set.
No, this calculator is designed for cold process bar soap using sodium hydroxide (NaOH). For liquid soap, potassium hydroxide (KOH) is used.