The saponification value (SAP value) is the amount of alkali (lye) required to completely saponify 1 gram of a specific oil or fat. It's expressed as milligrams of KOH or NaOH per gram of oil (mg/g). This is the most critical number in cold-process and hot-process soap making — it determines exactly how much lye you need to turn oils into soap without leaving excess lye in the final bar.

NaOH (sodium hydroxide) is used for solid bar soap, while KOH (potassium hydroxide) is used for liquid soap. KOH has a higher molecular weight, so you need more of it to saponify the same amount of oil. The approximate conversion is: KOH SAP ≈ NaOH SAP × 1.4025. Always use the correct SAP value for the type of lye you're working with. Our table provides both values for every oil.

The formula is simple: Lye needed (g) = Oil weight (g) × SAP value × (1 − Superfat %). For example, 500g of olive oil with a NaOH SAP of 0.135 and 5% superfat: 500 × 0.135 × 0.95 = 64.1g of NaOH. Use our built-in calculator above to do this automatically for any oil in the database.

Natural oils vary slightly in their fatty acid composition depending on factors like growing region, harvest season, processing method, and crop variety. This is why reputable sources provide SAP ranges (e.g., olive oil: 0.134–0.136 for NaOH). The calculator uses the midpoint average, which is safe for most recipes. For precision, always check your supplier's documentation if available.

Superfat (also called lye discount) is the percentage of oils intentionally left unsaponified in your soap. A 5% superfat means you use 5% less lye than the full saponification amount, leaving 5% of the oils as free moisturizing oils in the final bar. This provides a safety buffer against measurement errors and adds conditioning properties. Typical superfat ranges: 3–5% for body bars, 0–1% for laundry soap, 8–10% for facial bars.

Yes! Single-oil soaps are a great way to learn each oil's properties. Pure olive oil soap (Castile soap) is a classic — mild and gentle but requires a long cure (6+ months). 100% coconut oil soap produces abundant lather but can be drying without a high superfat (15–20%). Pure lard soap makes a hard, white, mild bar. Most artisan soapers blend multiple oils to balance hardness, lather, and conditioning.

Using a SAP value that's too low results in excess lye in your soap — this can cause skin irritation, burns, or a failed batch. Using a value that's too high means too little lye, leading to a soft, greasy bar that may go rancid quickly. Always double-check SAP values from reliable sources (like this tool) and run your recipe through a lye calculator before making soap.

Coconut oil (and palm kernel oil) contains a high percentage of short-chain and medium-chain fatty acids like lauric acid and myristic acid. Smaller fatty acid molecules have a higher ratio of carboxyl groups to total molecular weight, meaning more lye is needed per gram to saponify them. This is also why coconut oil creates such abundant, bubbly lather — those short-chain soaps are highly soluble in water.

A classic beginner recipe is the "Trinity of Oils": Olive Oil (40–50%) for mildness and conditioning, Coconut Oil (25–30%) for lather and hardness, and Palm Oil or Lard (20–30%) for a creamy, stable bar. These oils are affordable, widely available, and have well-documented SAP values. Start with small 500g batches, measure carefully, and always use a reliable SAP chart like this one.

A common guideline is a water-to-lye ratio of 2:1 (water = 2 × lye weight). This provides enough water to fully dissolve the lye while allowing the soap to set up properly. Beginners often use a 2.5:1 or 3:1 ratio for more working time. Advanced soapers may use a 1.5:1 "water discount" for faster curing. Our calculator suggests water at a 2:1 ratio by default. Note: water amount doesn't affect the saponification reaction — only the drying/curing time.