How to Use This Calculator
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1
Select your weight unit — grams or ounces. Use whatever unit your scale measures.
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2
Enter each oil weight. The default recipe is 500 g olive oil, 200 g coconut oil, and 300 g palm oil. Adjust to match your recipe and set unused oils to 0.
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3
Choose NaOH for solid bar soap or KOH for liquid soap.
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4
Set your superfat percentage. Five percent is a safe starting point for most recipes.
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5
Set water discount to 0% if you are new to soap making. Experienced makers may use 10–20%.
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6
Select your lye purity. Most NaOH pellets sold for soap making are 98% pure.
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7
Read the results — weigh out lye and water separately on a digital scale before mixing.
Why Each Oil Needs Its Own Lye Amount
Every oil is made of fatty acids, and different oils have different fatty acid profiles. Coconut oil is high in lauric and myristic acids. Olive oil is high in oleic acid. Palm oil is high in palmitic acid. Because these fatty acids have different molecular weights, each oil reacts with a different amount of sodium hydroxide. This ratio is called the saponification value, or SAP value.
Using too little lye leaves unreacted oil that makes the bar greasy and soft. Using too much leaves unreacted alkali — a caustic, unsafe bar. A soap calculator eliminates both risks by multiplying each oil weight by its own SAP value and summing the results.
SAP Values for Common Oils
| Oil | NaOH SAP value | KOH SAP value (100%) |
|---|---|---|
| Olive oil | 0.134 | 0.190 |
| Coconut oil | 0.190 | 0.267 |
| Palm oil | 0.141 | 0.198 |
| Castor oil | 0.128 | 0.180 |
| Shea butter | 0.128 | 0.180 |
| Sweet almond oil | 0.136 | 0.192 |
| Sunflower oil | 0.134 | 0.189 |
| Canola oil | 0.124 | 0.175 |
Example Calculation
Recipe total oils = 500 g olive oil + 200 g coconut oil + 300 g palm oil = 1,000 g
Olive oil NaOH = 500 × 0.134 = 67.0 g
Coconut oil NaOH = 200 × 0.190 = 38.0 g
Palm oil NaOH = 300 × 0.141 = 42.3 g
Total NaOH at 0% superfat = 67.0 + 38.0 + 42.3 = 147.3 g
Final NaOH at 5% superfat = 147.3 × 0.95 = 139.9 g
Adjusted for 98% purity = 139.9 ÷ 0.98 = 142.8 g NaOH to weigh
Water (38% of 1,000 g oils) = 380 g
Total batch = 1,000 + 142.8 + 380 = 1,522.8 g
What Is Superfat?
Superfat is the percentage of oils you leave unreacted by reducing the lye amount. A 5% superfat cuts the calculated lye by 5%, so a small portion of your oils passes through the soap unchanged. This makes the bar more forgiving — it is less likely to be lye-heavy — and can improve the feel on skin.
Most beginners use 5%. Higher superfat (above 8%) makes bars softer, reduces lather quality, and increases the risk of rancidity, especially with unsaturated oils like olive or sunflower. Recipes heavy in saturated fats (coconut, palm) tolerate higher superfat better.
What Is Water Discount?
The default water amount is 38% of total oil weight. A 20% water discount on a 1,000 g batch reduces water from 380 g to 304 g, raising the lye concentration. This helps bars unmold faster and slightly reduces cure time, but it also shortens working time — the batter reaches trace more quickly, which limits how much you can swirl or layer.
Start with 0% water discount for your first batches. Once you know how your recipe behaves, a 10–20% discount is a reasonable experiment.