Soap Recipe Calculator - Online Lye & Oil Saponification

Saponification is the chemical reaction between fats/oils and a strong alkali (lye) that produces soap. Each oil has a specific SAP value (saponification value), which indicates how much lye is required to fully convert that oil into soap. Using the correct amount of lye is critical—too little results in excess oils (superfat), while too much leaves unreacted lye in the soap, making it harsh or unsafe. Our calculator uses verified SAP values to ensure accurate measurements every time.

Superfat (also called lye discount) is the percentage of oils intentionally left unsaponified in your finished soap. This creates a gentler, more moisturizing bar. Common recommendations:

• 5-8% – Ideal for body and facial bars (gentle, moisturizing)
• 3-5% – Standard for most cold process recipes
• 0-3% – Best for laundry soap, dish soap, or cleaning soap
• Above 10% – May lead to soft bars and reduced shelf life (risk of rancidity)

Sodium Hydroxide (NaOH) produces solid bar soap. It creates a firm, long-lasting bar perfect for body and hand soap. Potassium Hydroxide (KOH) produces liquid or soft paste soap, commonly used for liquid hand soap, shampoo, and shaving cream. The SAP value differs between the two—KOH requires approximately 1.403 times more lye by weight than NaOH for the same oil blend. Our calculator automatically adjusts based on your selection.

The water-to-lye ratio affects trace time, curing time, and final bar hardness. Common ratios:

• 2.5:1 – The most widely recommended starting point (balanced trace time)
• 2.0:1 – Faster trace, firmer bars sooner (good for experienced soapers)
• 3.0:1 – Slower trace, more working time for intricate designs
• 1.5:1 or lower – Used in hot process soap or when dissolving lye with alternative liquids

Note: Always ensure enough water to fully dissolve the lye. A ratio below 1.2:1 may not dissolve all the lye properly.

SAP (Saponification Value) is the amount of NaOH (in grams) needed to saponify 1 gram of oil. Oils with higher SAP values (like coconut oil at 0.190) require more lye and produce harder, more cleansing bars. Oils with lower SAP values (like jojoba oil at 0.069) require less lye and contribute to gentler, more conditioning bars. A well-balanced recipe typically combines high-SAP oils for hardness and cleansing with low-SAP oils for mildness and moisturizing properties.

Bar hardness depends on your oil blend:

• Too soft? Increase hard oils (coconut, palm, shea butter, cocoa butter). These solidify at room temperature and contribute to bar firmness. Also check your water ratio—too much water lengthens cure time.
• Too hard/brittle? Reduce high-SAP oils like coconut and palm kernel oil. Add more conditioning oils like olive, sweet almond, or avocado oil for a smoother bar.
• Proper curing is essential—cold process soap needs 4-6 weeks to fully harden and become mild.

A digital kitchen scale with ±0.1g precision is highly recommended for soap making. Lye amounts must be measured accurately—even small errors can result in lye-heavy soap (harsh or unsafe) or overly superfatted soap (prone to rancidity). Always calibrate your scale before each session and use the "tare" function to zero out containers. For very small batches (under 300g total oils), consider a jeweler's scale (±0.01g) for the lye measurement.