How to Formulate a Soap Recipe

Learn how to formulate a soap recipe from scratch using oils, fats, lye, and soap additives. You’ll be guided through the different ways to create soap recipes and get instructions on using an online soap calculator. This guide is for creating natural cold-process soap recipes, but it also includes tips for hot-process soap recipes.

The first rule in formulating a soap recipe is that you can use practically any vegetable oil or animal fat to make soap—olive oil, coconut oil, and tallow, to name a few. However, creating a good soap recipe is a fine skill. With that skill comes learning to work with different ingredients and knowing how to choose the right balance of oils and the correct amount of lye, water, and additives.

I will take you through the main things to know as you head into creating natural soap recipes. They include choosing oils, making recipes more affordable or sustainable, and creating the best soap recipe for your purposes. I have plenty of soap recipes for you to use; however, formulating your own will give you far more flexibility and customization options. It also allows you to make soap within a budget, align with your ethos, or cater to allergies or a specific target market. You also get to create custom recipes that are entirely your own!

What Are Soap Recipes

Soap recipes are chemical formulas that transform everyday oils and fats into soap bars. They always include fatty oils, water, and lye, but can also include soap additives such as soap colorants, essential oils, herbal infusions, and botanicals.

Ingredients in soap recipes are listed by weight, with metric grams being the most common unit (Americans sometimes use ounces). When measuring soap ingredients, you must use a digital kitchen scale. If you use all-natural ingredients in the right quantities, your formulas will create gentle, natural soap.

You can make soap using either the cold process soap making method (CP) or the hot process (HP) method. Think of them as two ways to help you make the same soap recipe. The only significant difference between CP and HP soap recipes is the quantity of water needed. The processes may be different, but you still need a stick blender for both, as well as other equipment like eye protection, gloves, goggles, and other items.

A fun experiment you could try is to use the same recipe to make a batch of soap using either method. You’ll then see that both melt and introduce the ingredients in a way that initiates the saponification process. Due to the difference in process, finished hot process soap can often look more rustic than cold process, but not always. It’s fundamentally the same type of soap, though.

How to Formulate a Soap Recipe

When formulating a new soap recipe, you begin with a specific function or ingredients in mind. For example, you might want to make a gentle facial soap, or you have local honey that you’d like to use to make honey soap. This brainstorming phase is also helpful in looking at ingredient availability in your area and the best prices for oils and additives. You can also use this time to research ingredients suited to the formulation you have in mind and their ideal usage rates.

Once this legwork is complete, it’s time to get to the nitty gritty of formulating. Soap recipes are natural chemical formulas and should be adhered to as closely as possible. They include specific ratios of oils and the precise amount of lye that is necessary to transform the majority of the oils into soap.

Many soap makers use online soap calculators to formulate their soap recipes. However, they are only helpful if you know the principles of good formulation. We use three methods to calculate formulas: a general ratio method, fatty acid percentages, and considering recommended oil percentages. I use all three methods when formulating my soap recipes.

Single Oil Soap Recipes

Before we get to that, I’d like to touch on a common question in soapmaking: Can you use just one oil to make soap? You can, but there are only a few oils/fats that can be used alone to make good soap. The best single-oil soap recipes are Castile soap, made from 100% olive oil, and tallow soap, made from 100% beef fat. Another is 100% coconut oil soap.

Most soap recipes with just one oil/fat end up being too soft, too hard, too slimy, too cleansing, or have some other downside. Even Castile soap, an excellent soap, needs six months to a year to cure before it’s ready to use. Before this time, the lather is slimy, and the soap can have low cleansing. That’s why most soap recipes include several oils. Each oil brings different qualities to handmade soap and creates a much better result than using just a single type of oil.

Simple Soap Formulations

The most popular soap recipe formulas include common, affordable oils that create good soap. They are usually simple recipes that make good all-purpose soap for daily washing. If you’d like a little help with creating your soap recipes, here are some basic soap recipe formulations to start with. They only list the main soaping oils and provide their percentages as a total of all the oils used by weight. You would typically make them with a 5% superfat and a 33% lye concentration for your lye solution.

• 30% coconut oil, 30% sustainable palm oil, and 40% olive oil
• 35% olive oil, 25% babassu oil, 15% shea butter, 15% cocoa butter, and 10% castor oil
• 70% olive oil, 25% coconut oil, and 5% castor oil
• 60% lard or tallow, 20% coconut oil, 15% high-oleic sunflower oil, and 5% castor oil

Saturated to Unsaturated Fat Ratio

The simplest way that soap makers formulate simple soap recipes is by following a ‘sat:unsat’ ratio. Many are calculated to be around 50:50 in saturated fats to unsaturated fats, and they tend to include an average of four to six different oils. This ratio can vary based on the soap maker, with some preferring a 40:60 or 60:40 ratio, or something similar. Using the ratio method helps create soap recipes with relatively balanced qualities of hardness, longevity, conditioning, lather, and cleansing.

To clarify, saturated fats are typically “hard oils” solid at room temperature, and unsaturated fats are usually “soft oils” that are liquid at room temperature. Popular saturated fats in soap recipes are coconut, tallow, sustainable palm, palm kernel, and babassu oil. Common unsaturated fats include olive oil, sunflower oil, canola oil, avocado oil, and rice bran oil.

This basic way of looking at a soap recipe works for many soap-making oils, but not all. For example, castor oil, an unsaturated fat, is typically used at a rate of only 5-10% of the oils used. Using more than this can make the finished soap too soft and sticky. Using too much coconut oil can cause your soap to leave your skin feeling tight and over-cleansed. Too much sunflower oil can cause soap to go rancid quickly. Then you have solid oils like shea, cocoa, and mango butter that are a mix of saturated and unsaturated fats. They don’t neatly fit into one category or another.

Using the general ratio principle is helpful when creating a rough recipe draft. However, it needs refining by looking at ideal oil and fatty acid percentages in soap recipes.

Ideal Usage Rates of Oils in Soapmaking

As mentioned, few oils can be used alone to make good soap. Most soap recipes include four to six oils, each with different qualities that they bring to the finished soap bars. However, each oil has an ideal usage rate in soap, bringing enough qualities you’re looking for without any downsides. Using too much ordinary canola or sunflower oil can result in soap bars going rancid and developing Dreaded Orange Spots (DOS). Using too much coconut oil can make soap feel overdrying.

Oil/Butter	Main Fatty Acids	Soap Qualities	Ideal Usage Rate
Olive Oil	Oleic	Very conditioning, low lather, long-lasting	30–60%
Coconut Oil	Lauric, Myristic	Cleansing, bubbly lather, hard bar	15–25% (max 30%)
Palm Oil	Palmitic, Oleic	Hardness, creamy lather, stable base	20–30%
Castor Oil	Ricinoleic	Lather booster, conditioning, sticky in high %	3–8% (max 10%)
Shea Butter	Oleic, Stearic	Conditioning, creamy, adds hardness	5–25%
Cocoa Butter	Stearic, Oleic	Hardness, stable lather, conditioning	5–20%
Avocado Oil	Oleic, Palmitic, Linoleic	Conditioning, mild, nourishing	5–20%
Sweet Almond Oil	Oleic, Linoleic	Conditioning, silky feel, mild	5–15%
Sunflower Oil	Linoleic, Oleic	Light conditioning, soft bar	5–15%
High Oleic Sunflower Oil	Oleic (75–90%), Linoleic (low), Palmitic	Very conditioning, stable, resistant to rancidity	10–40%
Rice Bran Oil	Oleic, Linoleic, Palmitic	Conditioning, mild, may soften soap	5–20%
Lard	Oleic, Palmitic, Stearic	Hardness, creamy lather, conditioning	30–50%
Tallow	Oleic, Palmitic, Stearic	Hard, creamy, stable bar	30–50%
Mango Butter	Oleic, Stearic	Hardness, silky texture, light conditioning	5–15%
Canola Oil	Oleic, Linoleic	Conditioning, softer bar, short shelf life	5–15%
Grapeseed Oil	Linoleic, Oleic	Light, soft bar, oxidizes easily	5–10%

Formulate a Soap Recipe by Fatty Acid Percentages

You can create good soap recipes by looking at hard-to-soft oil ratios and ideal usage rates per oil. However, experienced soap makers also formulate by looking at the fatty acid percentages in a soap recipe. All oils are created from bonds of different fatty acids—think of them as molecular links in a chain that creates oils. I’ve listed the main fatty acids that you’ll find in specific oils in the above chart. In the chart below, you can see the ideal percentage of fatty acids in soap recipes and what they contribute.

Fatty Acid	Soap Qualities	Ideal % in Recipe	Oils High in this Fatty Acid
Lauric	Hardness, cleansing, bubbly lather	10–25%	Coconut oil, Palm kernel oil, Babassu oil
Myristic	Hardness, cleansing, bubbly lather (milder than lauric)	2–8%	Coconut oil, Palm kernel oil, Babassu oil
Palmitic	Hardness, creamy/stable lather	5–15%	Palm oil, Rice bran oil, Lard, Tallow, Cocoa butter
Stearic	Hardness, creamy lather, long-lasting bar	5–15%	Shea butter, Cocoa butter, Mango butter, Lard, Tallow
Ricinoleic	Lather booster, humectant, sticky in high %	3–10%	Castor oil only
Oleic	Conditioning, moisturizing, gentle lather	25–40%	Olive oil, High oleic sunflower, Avocado, Sweet almond, Lard
Linoleic	Silky conditioning, soft bar, prone to rancidity (DOS) in high %	5–15% (with care)	Sunflower (regular), Safflower, Grapeseed, Rice bran, Canola
Linolenic	Light conditioning, short shelf life, DOS risk in high %	<2%	Flaxseed, Hemp seed, Canola (to some extent)

Fatty Acid Information in Soap Calculators

When formulating using an online soap calculator, the fatty acid percentages per oil and the entire recipe should be provided. I use the free SoapCalc, and you can find this information both on the formulation screen and in the final recipe formula. Despite this, most beginner to intermediate soapmakers fixate on the ‘Soap Bar Quality’ section because it seems easier to understand.

However, the percentages of fatty acids are the most crucial information. Too much linoleic or linolenic acid can cause your soap to go rancid quickly. Too much oleic acid may cause the soap to initially be very soft or slimy when used. Ricinoleic acid in amounts over 10% can make the soap soft and sticky. Though you don’t have to stay strictly in the ideal ranges, beginners should do so until they understand what pushing the boundaries could do.

Using Fine, Exotic, and Expensive Oils to Make Soap

When beginner soapmakers use online soap calculators, they often get excited over the sheer number of oil selections. There’s meadowfoam oil, rose hip oil, hazelnut oil, and dozens others! My advice to those formulating is to be cautious. These oils are often expensive and, in some cases, heat-sensitive or have high levels of linolenic or linoleic acid. Both can potentially cause rancidification and funky smells in your soap.

That happened to me when I tried hemp seed oil in my soap. In weeks, my soap went from lovely to smelling like oil paints. It was very disappointing and such a waste. If you have fine oils to use, I usually recommend that you save them for making leave-on skincare products, such as skin cream or body balm. It’s better not to use them in soap making.

If you are sure you want to use a certain oil, make sure that it has a purpose in the soap. For example, neem oil soap suits those with eczema and psoriasis. Another thing to consider is that in cold process soap making, most of the fine oils you use will become soap—the superfat in soap will be a mixture of all the oils in the recipe. In hot process soapmaking, you have more control over the superfat. You can add a specific oil after the main soaping oils are cooked and fully saponified.

Calculating Superfat

Superfat is a simple but often misunderstood concept. When we formulate a soap recipe for personal care, we want it to be cleansing but gentle on our skin. To achieve this, we include enough lye in the recipe to fully transform the oils/fats we use into soap, but not enough to saponify them all. The extra oil left in each bar of soap is called the superfat.

Typically, we set our superfat level at around 5-7%, meaning 5-7% of the original oils stay in the bar as they are and don’t become soap. I don’t tend to use more than 6% superfat in my recipes, with 5% being plenty. It’s enough to give soap lovely conditioning, but not so much that it affects lather, the hardness of bars, or increases the chance of DOS.

Other soapmakers have different opinions and experiences, and some push the limits up to 10% or more. There are also cases when we want no superfat, such as when making solid dish soap recipes. Any residual oil in the soap can leave streaks on your dishes, cutlery, and glassware.

How Much Water to Use in Soap Making

One of the biggest questions I get about my natural soapmaking recipes is why my water amounts are different from the suggestions in soap calculators. Many people are surprised to learn that the amount of water (or water-based liquid) you use in soap recipes is variable and flexible. Each soapmaker will eventually have their preferences.

The amount of water set by default in soap calculators is commonly 38% of the weight of the soapmaking oils. This amount can make cold-process soap, but it will trace more slowly, gel quicker, and cause your bars to shrink in size during the curing stage. It’s a better amount of water for making hot-process soap because water evaporates while the soap cooks.

For most simple cold-process soap recipes, I either set the lye concentration at 33% or double the amount of lye (2:1 water to lye) needed to get the amount of water you need—either gives you roughly the same amount. It’s only when I want more time to work with the soap batter that I use more water than this. However, using more water can increase the chance of getting soda ash on the soap or issues like glycerine rivers or volcanoes.

The bare minimum amount of water you can use in soap recipes is equal to the weight of the lye. That would be a 50% lye concentration, and using it leads to the soap tracing more quickly, and gelling is less likely to happen, especially in non-loaf soap molds.

Calculating Soap Additives

Though some Soap Calculators include options for fragrance and soap additives, I ignore them. I don’t trust them to be accurate. Many fragrance oils (not natural) may have the same usage rates but that’s not the case for essential oils. There are also many essential oils, such as ylang ylang essential oil, with IFRA differences between manufacturers and essential oil types. I have guidance on how much essential oil to use in soap and encourage you to work it out manually, too.

Most other soap additives have a variable amount that you can use in soap recipes. Use a little, and you’ll get a small effect. Use more, and you’ll have a bigger impact. That includes exfoliants, natural colorants, and herbs and flowers. Finding the right balance between skin safety, desired effect, and stopping the additives from impeding lather and cleansing is part of learning to formulate.

Using a Soap Calculator

Each online soap calculator, also called a lye calculator, is different, but they are also the same. In essence, a soap calculator helps you see the fatty acid percentages, formulate a safe and good soap recipe, and scale up and down for batch sizes. It’s also crucial for calculating how much sodium hydroxide you need to make a batch of soap (or potassium hydroxide if you’re making liquid soap).

After formulating using a soap calculator, you should be able to save or print out a soap recipe. I tend to print them out and store the recipes I want to keep in a notebook.

If you’ve read this far, you’ll now know that there are three main ways to formulate a soap recipe. And that soap calculators help you formulate rather than create formulations for you. You can use it to set the superfat, to control the amount of water you want in a soap recipe, and to understand if your recipe will be good before you even make it.

How to Use the SoapCalc

Many soap calculators are either paid-for services or created by companies that sell soap ingredients, and I rarely dabble with those. Instead, I use the original and completely free SoapCalc, and even after all these years, it still works a treat. The interface is a bit archaic, and there’s a lot of information displayed, so I wanted to point out the main ways I work with it. The SoapCalc has seven areas that you work with and are numbered:

1. The first area is where you select NaOH (sodium hydroxide) to formulate a cold-process soap recipe. The other selection, KOH (potassium hydroxide), is for making liquid soap.
2. The second area is where you select your weight measurement. I recommend that you stick with grams since its increments on digital scales are smaller than ounces/pounds and help you get a more accurate measurement. You can also set your batch size here—the smallest batch size I recommend making is 454 g (1 lb).
3. The amount of water in soap recipes is relatively flexible. In the third part of SoapCalc, you choose how the water amount in your recipe is calculated. I tend to select the lye concentration, and for most simple soap recipes, I use 33%. That means that lye makes up 33% of the lye solution with water making up the other 67%. With this way of measuring, the highest you can go is 50%, and the lowest is 25%, but there’s very little reason to go that high or low.
4. You choose the superfat level in your soap in part four. 5% is usually very good for most soap recipes. Don’t go crazy here since higher superfats can sometimes cause performance and longevity issues. I completely ignore the fragrance field in this area, too. I work out how much essential oil to use manually.
5. Section five displays fatty acids and oil types. Click an oil to see its fatty acid percentages. Double-click an oil to see it appear in the soap recipe oils section in section six. There are other fields here, too, but they won’t display information until you finish the next section.
6. Your oil formulation appears in section six. Use the radio buttons to select whether the amount of that oil will be calculated by percentage or by weight. For example, if you want to make a recipe with 100% olive oil, you would select percentages. If you only have 500 g of olive oil left and want to use it up in a batch of soap, you’d use the other radio button.
7. Once you’ve added all your oils in section six, press ‘Calculate Recipe’ in section seven. Then, you can see the saturated to unsaturated ratio back in section five (it’s at the bottom). You can also see the complete fatty acid percentages of the entire recipe in section five. It’s in the second column, ‘All’. When you’re happy with the recipe, press the button View/Print Recipe in section seven.

A Recommendation for Beginners

I hope this piece has answered some questions and helped you learn how to formulate a soap recipe. If you have any questions, please leave me a comment below.

Another thing… Formulating soap can be a creative but complex topic, and unless you have experience making soap already, I don’t recommend that you start formulating just yet. If you make a mistake and your first batch of soap ever fails, was it you or the recipe? You might never know. It’s a bit like learning to bake a cake. Why reinvent the wheel and potentially set yourself up for failure when you can use a tried-and-tested recipe?

If you are a beginner, I recommend that you try some of the easy soap recipes here on Lovely Greens and enroll in my online soapmaking course. Once you’ve learned the basics of making soap, you’ll understand what to expect. That way, you’ll be better prepared to create your own formulations!

More Soapmaking Inspiration

• Ultimate guide to Soap Molds (silicone molds, etc)
• Soapmaking Safety Guidelines
• How to Customize a Soap Recipe
• Lovely Greens Soapmaking Course