Lye Calculator
Calculate the exact amount of lye (sodium hydroxide) needed to saponify oils for soap making, based on your chosen oils and superfat percentage.
Published by:
isCalculator Editorial Team
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How to Use the Lye Calculator
This calculator determines the amount of sodium hydroxide (lye) needed to saponify a given oil, accounting for a superfat percentage. All inputs must be in grams (metric system).
- Select an oil from the dropdown. Each oil has a fixed saponification value (shown in parentheses).
- Enter the oil weight in grams (e.g., 500). Must be a positive number.
- Set the superfat percentage (0–30%). Default is 5%. Superfat leaves some oil unsaponified for skin benefits.
- Click "Calculate Lye". The result shows the exact lye weight in grams, plus the formula used.
Formula: Oil Weight × Saponification Value × (1 − Superfat/100)
Example: 500 g olive oil (0.134) with 5% superfat → 500 × 0.134 × 0.95 = 63.65 g lye.
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Frequently Asked Questions
A lye calculator helps soap makers determine the precise amount of sodium hydroxide (lye) needed to saponify a given amount of oils, based on the saponification value of each oil and desired superfat.
Select an oil from the dropdown, enter the weight of that oil in grams, and set your desired superfat percentage (default 5%). Click 'Calculate Lye' to get the required lye amount.
Superfat is the percentage of oils that remain unsaponified in the soap, providing moisturizing properties. A typical range is 5-10%.
This calculator handles one oil at a time. For multiple oils, calculate each separately and sum the lye amounts.