SAP Values Explained: The Complete Guide for Soap Makers

Quick Answer

SAP (saponification) value tells you how much lye is needed to convert a specific oil into soap. For sodium hydroxide soap: multiply oil weight by its NaOH SAP value. Example: 16 oz olive oil × 0.134 = 2.14 oz lye needed. Every oil has a unique SAP value based on its fatty acid composition.

What Is a SAP Value?

SAP value (saponification value) is a number that represents how much alkali (lye) is required to saponify a specific amount of oil or fat. Different oils have different fatty acid compositions, so they require different amounts of lye. Learn how to use these values in our complete lye calculation guide.

The chemistry: Oils are made of triglycerides (fatty acid chains attached to glycerin). Lye breaks these bonds, freeing the glycerin and converting fatty acids into soap. Different fatty acids require different amounts of lye.

Types of SAP Values

NaOH SAP Value (Sodium Hydroxide)

Used for: Bar soap (cold process, hot process)

This tells you ounces of sodium hydroxide needed per ounce of oil.

Example: Olive oil NaOH SAP = 0.134

• 1 oz olive oil needs 0.134 oz sodium hydroxide

KOH SAP Value (Potassium Hydroxide)

Used for: Liquid soap, cream soap

This tells you ounces of potassium hydroxide needed per ounce of oil.

Example: Olive oil KOH SAP = 0.188

• 1 oz olive oil needs 0.188 oz potassium hydroxide

Converting Between NaOH and KOH

KOH SAP = NaOH SAP × 1.403
NaOH SAP = KOH SAP × 0.713

Complete SAP Value Reference Table

Vegetable Oils

Butters

Animal Fats

How to Use SAP Values

Step 1: List Your Oils and Weights

Example recipe:

• Olive Oil: 10 oz
• Coconut Oil: 4 oz
• Shea Butter: 2 oz

Step 2: Multiply Each by SAP Value

• Olive Oil: 10 × 0.134 = 1.340 oz lye
• Coconut Oil: 4 × 0.178 = 0.712 oz lye
• Shea Butter: 2 × 0.128 = 0.256 oz lye

Step 3: Sum the Results

Total lye at 0% superfat: 1.340 + 0.712 + 0.256 = 2.308 oz

Step 4: Apply Superfat Discount

For 5% superfat (learn more in our superfat calculator guide): 2.308 × 0.95 = 2.19 oz sodium hydroxide

Why SAP Values Vary

Natural Variation

Oils from the same plant can have slightly different fatty acid profiles based on:

• Growing conditions
• Harvest timing
• Processing method
• Geographic origin

This is why SAP values have ranges, and calculators use accepted averages.

Refinement Level

Virgin, refined, and pomace versions of the same oil may have slightly different SAP values. Most calculators use the most common version.

Temperature Variations

Some oils (like coconut) have different grades based on melting point:

• Coconut 76 degrees (standard): 0.178
• Coconut 92 degrees (fractionated): 0.170

Important SAP Value Concepts

Superfat and SAP Values

Superfat means using less lye than the SAP calculation indicates. This leaves some oil unsaponified in the finished soap.

Formula with superfat:

Lye Amount = (Sum of oil × SAP) × (1 - superfat%)

Blended Oils

For pre-mixed oils (like a supplier's soap blend), you need the blend's specific SAP value from the supplier. You can't calculate it without knowing the component oils and their proportions.

Missing SAP Values

If you can't find a SAP value for an exotic oil:

1. Contact the supplier
2. Use a similar oil as a substitute
3. Don't use it until you have accurate data

Never guess SAP values. Incorrect values create lye-heavy (dangerous) or lye-light (failed) soap.

Common SAP Value Mistakes

Using KOH Values for Bar Soap

KOH values are higher than NaOH values. Using KOH SAP with sodium hydroxide creates lye-heavy soap.

Using NaOH Values for Liquid Soap

NaOH values are lower than KOH values. Using NaOH SAP with potassium hydroxide creates soft, failed liquid soap.

Forgetting Unit Consistency

If your SAP value is per gram, your oil weight must be in grams. Mixing ounces and grams creates massive errors.

Using Outdated or Incorrect Sources

SAP values vary slightly between sources due to natural oil variation. Use one consistent source for all calculations.

Oils With Special Considerations

Jojoba Oil

SAP value: 0.066 (very low)

Jojoba is technically a liquid wax, not an oil. It has a much lower SAP value and doesn't fully saponify like true oils. Use at low percentages (5-10%).

Beeswax

SAP value: 0.067

Beeswax adds hardness but doesn't saponify well. Use small amounts (2-5%) primarily as an additive.

Lanolin

SAP value: 0.074

Similar to jojoba—not a true oil. Adds conditioning but use sparingly.

Castor Oil

SAP value: 0.128

Unique fatty acid profile (ricinoleic acid) creates bubbly lather. Usually used at 5-10%.

Frequently Asked Questions

Where do SAP values come from?

SAP values are determined through laboratory testing. A known amount of oil is fully saponified, and the lye required is measured. Published values are averages from many tests.

Why do different calculators sometimes give different lye amounts?

Different SAP value databases exist, with slight variations due to natural oil differences. Use one consistent calculator for your batches.

Can I calculate the SAP value for my homemade oil?

Not easily. SAP determination requires laboratory equipment. For homemade or home-rendered oils, use published values for that oil type as an approximation.

What if an oil isn't in the SAP chart?

Contact your supplier for SAP data. If unavailable, research what similar oils are or avoid using it until you have accurate information.

Do I need to memorize SAP values?

No. Soap making software and online calculators store SAP values and do the math for you. Understanding what they mean is more important than memorization.

Are SAP values the same worldwide?

Yes, the chemistry is universal. However, different regions may use different average values based on locally sourced oils.

Conclusion

SAP values are the foundation of accurate soap making. They tell you exactly how much lye is needed to transform each oil into soap. Using correct SAP values ensures safe, balanced bars every time.

While understanding SAP calculations is valuable, most soap makers rely on software or calculators that have SAP databases built in. The calculator handles the multiplication and summing; you focus on creating great recipes.