Soap Calculator: Complete SoapCalc Guide

TL;DR: SoapCalc is a free tool for calculating NaOH from oils. Without the calculator it is not possible to find the correct amount of lye - the key is the saponification number of each oil. The wizard explains all fields in English.

The Soapmaking Calculator is a must-have tool for anyone making soap using the cold process or hot process method. Without it, it's impossible to know exactly how much caustic soda to add to a recipe - and any mistakes in the dosage of lye will result in soap that is either caustic (too much NaOH) or undrying and soft (too little).

This page will guide you through the most widely used calculator - SoapCalc (soapcalc.net) - step by step with explanation of each field in Czech. After reading you will be able to enter your own recipe and understand the results.

Why you need a calculator

You cannot enter a prescription without the calculator. Each oil has different saponification number (SAP) - the amount of NaOH in grams required to saponify 1 gram of the fat in question. For example:

• Coconut oil: SAP = 0.178
• Olive oil: SAP = 0.134
• Beef tallow: SAP = 0,140
• Castor oil: SAP = 0.128

For a recipe with a mix of oils, you need to calculate the weighted sum of the SAP values of all ingredients, subtract the super fat and convert to the amount of water. This can be done manually (see our page Chemistry of saponification), but the calculator is faster and eliminates errors.

Key point: always use the calculator for each new or modified recipe. Even a small change in the ratio of oils changes the amount of NaOH required.

SoapCalc: the most popular free tool

SoapCalc (soapcalc.net) is a free online calculator available since 2001. It contains a database of over 170 oils and fats, automatically calculates soap properties and exports recipes. It is available in English, but you can do without with this guide.

Alternatives:

• SoapMaker 3 (placeware, Windows) - professional software for soapmakers
• Brambleberry Lye Calculator - simpler interface, less oil in the database
• LyeCalc (iOS, Android) - mobile app

For beginner and intermediate soapmakers, SoapCalc is ideal. In the guide we focus on it.

Navigating SoapCalc: page overview

When you open soapcalc.net you will see three main sections:

Top: recipe settings - type of soap, weight of oils, water, super fat, perfume.

Middle section: selection of oils - an alphabetical list of the oils you enter in the recipe.

Lower part: results and properties - table of soap properties + finished recipe in grams.

Step by step: entering a recipe

Which type of lye to choose?

Field „Lye“ - dropdown menu:

• NaOH = sodium hydroxide → solid soap (bar soap)
• KOH = potassium hydroxide → liquid soap or paste

For solid cold process soap always select NaOH.

How to enter oil weight?

Field „Weight of Oils“ - enter the total weight of the oils in your recipe here.

Dropdown for units: Grams (grams) or Ounces (ounces).

Example: if your recipe contains 700 grams of total oils, enter 700 and select Grams.

Tip: Start with a total weight of 500 g or 700 g - this is suitable for a standard loaf tin (about 8-10 pieces).

How to set water (Water as % of Oils)?

Field „Water as % of Oils“ determines the amount of water as a percentage of the total weight of the oils.

Standard value: 33-38 %

• 38%: more water = more liquid trace = longer maturation. Suitable for complex design techniques (swirly, layers).
• 33%: less water = faster solidification = shorter maturation. Suitable for cleaner soaps.
• 28-30% (water discount): even less water = very fast trace, shorter maturation, harder soap. Recommended for the more experienced.

For the first recipes enter 36-38 %.

How to set superfat?

Field „Super Fat“ (or "Lye Discount“) - the percentage of oils that do not react with lye.

Standard value: 5%

• 0-3 %: hard cleaning soap (laundry bar), washing bar
• 5%: standard for most recipes
• 8-10%: milder, conditioning soap for sensitive skin
• 15-20%: only for 100% coconut soap

For the first recipes enter 5.

What is the fragrance ratio?

Field „Fragrance Ratio (oz/lb)“ - the amount of perfume or essential oil in ounces per pound of oils.

Standard value: 0.4-0.7 oz/lb (approximately 2.5-4.4%)

For essential oils: 0.4-0.5 oz/lb (2.5-3.1%) For perfume oils: 0.5-0.7 oz/lb (3.1-4.4%)

SoapCalc calculates the amount of perfume automatically.

How to choose oils?

In the middle of the page is an alphabetical list of oils. Click on the oil you want to add - a form will open to enter the quantity.

Method of entry: percentages or grams (according to the settings at the top).

Recommendation: Enter as a percentage - then you can easily adjust the total weight without recalculating.

An example of a simple recipe:

• Coconut Oil: 30%
• Olive Oil: 40%
• Sunflower Oil: 20%
• Castor Oil (castor): 10%

Total: 100%.

After entering each oil, click „Add“ or Enter. The oils will be added to the recipe list.

How to run the calculation?

Click on „Calculate Recipe“ (or a button with a similar name).

What do the individual results mean?

SoapCalc displays a table of soap properties. Here is an explanation of each value:

Hardness: recommended range 29–54

The hardness of the finished soap defines how hard the soap will be. High hardness = the soap is firm, tolerates moisture well. Low hardness = softer, quicker to use.

It is affected by: saturated fatty acids (palmitic, stearic, lauric). Coconut oil, tallow, palm butter, cocoa butter all increase hardness.

Cleansing: recommended range 12–22

Ability to remove dirt and grease. Too high a value (above 25) = drying. It is affected by lauric and myristic acid - mainly coconut and palm kernel oil.

Conditioning: recommended range 44–69

Conditioning properties for the skin. Influenced by oleic, linoleic and ricinoleic acid. Olive oil, sunflower oil, castor oil - increase conditioning.

Bubbly (lather): recommended range 14–46

Ability to form foam. It is affected by lauric, myristic and ricinoleic acid. Coconut oil and castor oil - the main contributors.

Creamy: recommended range 16-48

Density and creaminess of the foam. It is affected by palmitic and stearic acid. Tallow, cocoa butter, palm butter.

Iodine Value: recommended range 41-70

It measures the proportion of unsaturated fatty acids. High value = more unsaturated acids = soap can yellow more easily (oxidation). Olive, linseed, hemp oil - high value. Coconut, tallow - low.

INS Value (Iodine-NaOH-SAP): recommended range 136-170

The overall score of the "quality“ of the recipe according to SoapCalc. Values outside the range are not automatically bad - they are recommendations, not prohibitions.

Practical example: basic recipe

Let's enter a specific recipe:

Basic CP recipe (700 g of oils):

• Coconut oil: 35% (245 g)
• Olive oil: 35% (245 g)
• Sunflower oil: 20% (140 g)
• Castor oil: 10% (70 g)

Settings in SoapCalc:

• Lye: NaOH
• Weight of Oils: 700 g
• Water as % of Oils: 36 %
• Super Fat: 5%
• Fragrance Ratio: 0.5 oz/lb

Resulting recipe (SoapCalc):

• NaOH: ~100 g
• Water: ~252 g
• Perfume/EO: ~22 g

Features:

• Hardness: ~43 ✓
• Cleansing: ~23 (slightly above recommendation - reduce coconut to 30%)
• Conditioning: ~53 ✓
• Bubbly: ~38 ✓
• Creamy: ~24 ✓
• INS: ~155 ✓

(The exact values depend on the version of SoapCalc and the SAP value database used.)

How to adjust the recipe according to the results

Too low hardness (below 29): Add coconut oil, tallow, cocoa or shea butter.

Too high cleansing value (above 22): Reduce the proportion of coconut or palm kernel oil. Replace with olive, sunflower or hemp oil.

Low conditioning (below 44): Add olive, sunflower or avocado oil. Add castor oil (increases conditioning and bubbles).

High iodine (above 70): Soap may have a shortened shelf life due to oxidation. Add an antioxidant (vitamin E, rosemary extract - ROE) or reduce the proportion of linseed/hemp oil.

Water discount: when and how to use

Water discount means a reduction in the standard amount of water (usually below 33%). It is used for:

• Faster solidification - the soap is finished earlier (suitable for sale)
• Harder resulting soap - less water = less space for water channels in the structure
• Reducing the risk of soda ash - less water on the surface = less oxidation
• Recipes with sugars (honey, milk) - sugars add moisture, water discount compensates

Recommendation for beginners: do not use water discount for the first recipes. Less water = faster trace = less time for complicated techniques. Start with 36-38% water.

Tips for working with SoapCalc

Save the recipe: SoapCalc does not have a login, but the URL is updated with the recipe - copy the URL to save. Or export the recipe (Print/PDF button) to PDF.

Compare recipes: Try entering different ratios and watch how the properties change. This will help you understand how each oil contributes to the result.

Start with the result: If you know you want a hard, good lathering soap - look at the ranges for hardness and bubbles and back-build the oils.

Database of SAP values: SoapCalc works with average SAP values for each oil. The values vary slightly between different sources (different varieties, production processes). Therefore, test the final soap for pH - see What is cold process.

Frequently asked questions

Do I have to usar a calculator or can I take calculate it myself? You can, but it's error-prone. Calculating SAP values for a mix of oils is tedious. The calculator saves you time and eliminates errors.

What is the difference between NaOH and KOH? NaOH produces solid soap, KOH liquid. In the cold process, NaOH is always used. KOH is used for liquid soaps and pastes.

Why is super fat important? Super fat leaves unsaponified oils in the soap that condition. Without it, the soap would burn the skin. The standard is 5% - without it the soap cleans better, with more SF it will be softer and last longer.

What water is used? Distilled or filtered. Tap water contains minerals that can impair the calculation. It's not worth buying special water - distilled is cheap.

Can I use the results from one calculator in another recipe? Generally yes, but SAP values vary slightly. If you take the recipe recalculated in SoapCalc in another calculator, the NaOH differs slightly (by 1-2 g). Superfat compensates for this.

See also:

• Chemistry of saponification - how to manually calculate SAP without a calculator
• Calculator comparison — SoapCalc vs. Brambleberry vs. SoapMaker 3
• Your first recipe - recipe ready to be entered into the calculator
• Oil encyclopedia - SAP values and properties of all oils