Free Soap INS Value Calculator — Hardness & Lather Balance

Soap INS Value Calculator

Select up to 6 oils and enter their percentages to calculate your soap recipe's INS value — a score of 145–170 indicates a well-balanced bar with good hardness and lather.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Input the sum of (oil percentage × oil INS value)
For each oil in your recipe, multiply its percentage (as a decimal) by its individual INS value. Sum these results for all oils to get your total 'Sum (% × Oil INS)'.
2
Review the calculated INS Value and Rating
The calculator will instantly display your recipe's overall INS Value and a qualitative rating, such as 'Good' or 'Hard / Drying', to guide your formulation.

Example Calculation

A small-batch soapmaker wants to evaluate the hardness of a new recipe containing coconut, olive, and shea oils.

Sum (% × Oil INS)

148

Results

INS Value

148, Rating: Good

Tips

Adjusting for Desired Hardness

If your calculated INS value falls below the 'Acceptable' range (130-145), consider increasing the percentage of harder oils like coconut or palm, or reducing softer oils like olive, to achieve a firmer bar.

Balancing Cleansing and Conditioning

Aim for an INS value between 145 and 170 for a good balance of cleansing and conditioning properties. Values above 170 can lead to overly drying soap, while those below 130 may result in a soft bar that cures slowly and dissolves quickly.

Impact of Superfatting

Remember that while the INS value reflects the base oil composition, superfatting (adding extra unsaponified oils) can slightly soften the final bar and enhance conditioning. Most cold process soap recipes use a 5-8% superfat.

Unlocking Soap Chemistry: Calculating Your Recipe's INS Value

The Soap INS Value Calculator is a fundamental tool for artisan soapmakers, providing a crucial metric to predict the overall hardness, lather, and conditioning profile of a soap bar. By inputting the percentages of up to six different oils, this tool computes a combined INS value, with an ideal target range of 145–170 for a balanced, high-quality cold process soap. This insight is vital for formulating new recipes and ensuring consistency in production in 2025.

Balancing Soap Properties with the INS Value

The INS value (Iodine Number Saponification) serves as a quick reference for the overall characteristics of a soap recipe. It combines an oil's saponification value (how much lye it needs) and its iodine value (its degree of unsaturation). A higher INS suggests a harder bar with more stable lather, while a lower INS indicates a softer, more conditioning soap. The 145-170 range is desirable because it balances these properties, yielding a bar that is firm, long-lasting, and produces a satisfying creamy and bubbly lather, without being excessively brittle or too soft. For example, a soap with an INS below 120 might be too soft, while one above 200 could be overly brittle.

The Math Behind the INS Value Calculation

The INS value for a soap recipe is a weighted average of the individual INS values of the oils used. While the exact formula for each oil's INS value can be complex, for a blend, it's calculated as:

Recipe INS = (Oil1 % × Oil1 INS) + (Oil2 % × Oil2 INS) + ...

Where:

OilX % is the percentage of a specific oil in your total oil blend.
OilX INS is the known INS value for that particular oil.

For instance, Coconut Oil has an INS of approximately 258, Palm Oil around 145, Olive Oil about 106, and Castor Oil around 95. The calculator sums these weighted contributions to provide the final recipe INS.

💡 To further refine your soap's characteristics, use our Soap Iodine Value Calculator to specifically assess hardness, conditioning, and shelf life.

A Worked Example: Calculating a Blend's INS

Let's evaluate a common four-oil soap recipe with a total oil weight of 32 oz:

Coconut Oil: 30% (INS ~258)
Palm Oil: 30% (INS ~145)
Olive Oil: 30% (INS ~106)
Castor Oil: 10% (INS ~95)

To calculate the overall INS value:

Step 1: Multiply each oil's percentage by its INS value.
- Coconut: 0.30 × 258 = 77.4
- Palm: 0.30 × 145 = 43.5
- Olive: 0.30 × 106 = 31.8
- Castor: 0.10 × 95 = 9.5
Step 2: Sum these contributions. Recipe INS = 77.4 + 43.5 + 31.8 + 9.5 = 162.2

The resulting INS value is 162.2, which falls comfortably within the ideal 145–170 range, indicating a well-balanced soap with good hardness and lather.

💡 Once you've perfected your oil blend, use our Soap Oil Blend Recipe Calculator to get exact weights for your batch.

Limitations of the INS Value Metric

While the INS value is a valuable predictive tool, it's essential to understand its limitations. The INS value primarily provides a theoretical prediction of a soap's characteristics, and real-world results can sometimes vary. For instance, recipes with very high superfat percentages (e.g., above 10%) or those containing unique additives like sugar (which can soften a bar) or salt (which hardens it) may behave differently than their INS value suggests. Furthermore, the INS value doesn't account for the impact of cure time; even a theoretically perfect INS value won't yield a great bar if it hasn't cured sufficiently. It's also a general metric and doesn't differentiate between bubbly and creamy lather types. Therefore, the INS value should be used as a guideline in conjunction with other metrics like the Iodine Value and actual testing, rather than an absolute predictor of soap quality.

Frequently Asked Questions

What does INS stand for in soap making?

INS stands for Iodine Number Saponification. It's a combined metric used to predict the hardness and longevity of a finished soap bar, derived from the iodine value (a measure of unsaturation) and saponification value (how much lye is needed) of the oils used. An ideal INS value typically falls between 130 and 170.

Why is a high INS value not always desirable?

While a higher INS value generally indicates a harder, longer-lasting bar, values exceeding 170-180 can lead to soap that is overly cleansing and potentially drying to the skin. Oils like coconut oil, with an INS value around 250, contribute significantly to hardness but need to be balanced with softer, more conditioning oils.

How does the INS value relate to a soap's cure time?

Soaps with lower INS values (e.g., below 130) tend to be softer and require a longer cure time, often 6-8 weeks, to fully harden and evaporate excess water. Conversely, soaps with higher INS values (e.g., 170+) will typically harden faster and may be ready in 4-6 weeks, though a full cure is always beneficial for longevity.

Can I use the INS value to predict lather?

The INS value primarily predicts hardness and cleansing properties, not directly lather. However, oils that contribute to a high INS value (like coconut oil) often produce abundant, bubbly lather. For creamy, stable lather, you'd also consider oils like castor oil, which has a low INS but excellent lather-boosting properties.