Lye Soap Recipes, SAP Values And Formula

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We have a lot of soap tutorials to get started making a batch of DIY soap right away, but have you considered experimenting a little? Working with SAP values for your lye soap recipes and calculating the amount of water required may seem a little complicated at first glance but it really isn’t.

adding lye make homemade soap

Working Your Lye Soap Recipes

All you actually need are the Sap values of the oils you are using which I’ll give you in the chart below. With these values and a calculator, which most people now have on their computers and mobiles! You can experiment with soapmaking and its so much fun!

You could simply use a lye soapmaking calculator, I have one here in the member’s area, along with a comprehensive formulation guide. However, by working this through yourself you will gain a better understanding of lye soap recipes and how to make soap at home.

Step 3: Pour into your soap mold

Soap Calculator & Formulation Guide

Select your chosen oils, along with the weight or percentage. The soap calculator will then show the total weight of lye and water required. The result can be instantly adjusted by changing your preferred superfatting level or water/lye ratio.

The Method

Caution: Be very careful handling and mixing the lye. It is extremely caustic and can burn if it gets and stays on the skin. If at any point you spill or splash lye or caustic soap batter onto your skin, wash it off with lots of water right away. You can also use some kind of vinegar or lemon juice to calm the burning and wash away the lye, then rinse thoroughly with water. Remember that lye is alkaline, not an acid, and so a gentle acid should help to neutralize the lye. If this doesn’t help, seek advice from a medical professional as soon as possible.

The most important element when making lye soap is the SAP Value (saponification values) of your oil. Saponification is the reaction that takes place to make your soap.

The SAP Value of a chosen oil allows you to calculate the correct amount of Lye (Sodium Hydroxide – NaOH) needed to fully saponify it when making homemade soap using cold process.

If you search online you will find a host of online soap calculators. But to me as a beginner, they all seemed very complicated. So much so that after learning this process, I went ahead and built a much simpler soap calculator for savvy homemade along with a comprehensive formulation guide.

But I digress,

So back in the day, for my own peace of mind I had to understand what was going on… Folks, it turns out that this is not rocket science, it’s as simple as baking a cake. Here’s how I do it…

How Much Lye?

soap making lye
Soap Making Lye (NaOH – Sodium Hydroxide)

Simply decide on the weight of each oil in your lye soap recipe then multiply each oil by the given factor in the chart saponification chart below to see how much Lye (alkali) you need to add.

You can use either grams or ounces, I use grams for soapmaking as its more accurate, check out more info on measuring here. First calculate the lye for each oil independently, then add them all together to get an overall weight of lye required to saponify the oils.

Lye Soap Formula Example:

Ingredients here are taken from my basic soap recipe, we simply multiply the grams of each oil by the SAP value in the chart below.

  • Olive Oil – 500g X 0.134 = 67g Lye.
  • Coconut Oil – 300g X 0.190 = 57g Lye.
  • Palm Oil – 200g X 0.141 = 28.2g Lye.

Total Lye Required To Saponify Oils = 152.2g

But Remember This: So far we have simply calculated that it takes exactly 152.2g of Lye to saponify our oils, but we cant actually use the whole 152g, there would be zero room for error. The calculation is so exact that if we stick to 152g once all the ingredients were completely saponified your soap could still be too caustic and harsh. Below is how we use supperfatting to help.

Superfatting Your Lye Soap (Lye Discounting)

After you have calculated the exact amount of lye required to saponify the oils in your lye soap recipe you need to discount the lye by between 2% and 10% (I recommend 5%). This will leave a little excess fat remaining in your soap and ensure all of the caustic alkali has been eradicated. If you don’t use superfatting the soap could be far too harsh and still caustic.

The key is to have a nice balance. If you end up with too much oil/fat left un-saponified you could be left with a soap that’s too soft. If you have too little left it can be way too harsh.

In general for a softer soap discount more, for harder soap discount less (between 2% and 10%). To be sure that you have a good PH balance always test soap using a ph strip to make sure it is somewhere between 7-10.

In Our Basic Soap Example:

  • The Lye Required To Saponify was 152.2g
  • 5% of 152.2g = 7.61g
  • 152.2 minus 7.61 = 144.59g

Lye To Add = 145g (rounded up from 144.59g)

How Much Water?

Add Lye to Oils Make Homemade Lye Soap
Adding Lye To Oils When Making Homemade Lye Soap

The other element is the amount of water used, Lye is added to this water before mixing with the oils. This element is much more flexible, it’s very much open to debate and more of a preference issue.

As a general rule, you should be using one of two options. You can calculate water as between 30% and 35% of the total weight of the ingredients used. Or you can calculate it as water to lye ratio, both options work, it just depends on which you prefer.

When starting your soap making journey its best to have more water than not enough.

The more water you have means more time you have to make the soap and more room for error. But this also means that the soap can take longer to cure and sometimes its softer for longer. As you gain more experience you can reduce the water level to speed up the process.

As an example, these days I’m using option 2 (below) with a Water Lye ratio of 2/1. For me, this is a simple calculation and makes the best soap (I just x2 my Lye). But I wouldn’t start with that, if it’s your first time, go with 2.5/1 and take a little longer.

So as you can see with the options below, the water is more of a preference and experience issue, unlike calculating the lye value it’s not ‘set in stone’.

Option 1

In Our Basic Soap Formula Example:

  • All oils weighed 1000g
  • After superfatting Lye was calculated at 145g
  • Total Weight = 1145g
  • 33% or divided by 3 = 381g

Water To Add = 381g 

Option 2

In Our Basic Soap Formula Example:

  • After superfatting, Lye was calculated at 145g
  • Using a Water to Lye ratio of 2.5/1
  • 145 x by 2.5 = 362.5g

Water To Add = 363g 

My Calculation (experienced soap makers)

In Our Basic Soap Formula Example:

  • After superfatting, Lye was calculated at 145g
  • Using a Water to Lye ratio of 2/1
  • 145 x by 2 = 290g

Water To Add = 290g 

Saponification Chart

Sodium Hydroxide (NaOH) – Caustic Soda

Beeswax – 0.069
Carnauba Wax – 0.069
Candelilla wax – 0.039
Lanolin – 0.0741
Almond-Sweet – 0.136
Apricot kernel – 0.135
Arachis – 0.136
Avocado – 0.133
Babassu – 0.175
Beef Tallow – 0.1405
Borage Oil – 0.136
Brazil Nut Oil – 0.175
Butterfat (cow) – 0.1619
Butterfat (goat) – 0.1672
Camelia oil – 0.136
Castor oil – 0.1286
Chicken fat – 0.1389
Chinese Bean – 0.135
Cocoa Butter – 0.137
Coconut (refined) – 0.190
Coconut (virgin) – 0.1946
Cod Liver Oil: 0.1326
Coffee Seed Oil – 0.130
Colza – 0.124
Corn (Maize) – 0.136
Cottonseed – 0.1386
Deer Tallow – 0.1379
Earthnut – 0.136
Evening Primrose – 0.136
Flaxseed – 0.1357
Gigely Tree – 0.133
Goat Tallow – 0.1383
Goose Fat – 0.1369
Grapeseed – 0.1265
Grapefruit Seed Oil – 0.135
Hazelnut – 0.1356
Hemp Seed – 0.1345
Herring Oil – 0.136
Illippe Butter – 0.136
Jojoba – 0.069
Kapok – 0.137
Katchung – 0.136
Kokum Butter – 0.134
Kukui Nut – 0.135
Lard – 0.138
Linseed – 0.1357
Loccu – 0.134
Macadamia Nut – 0.139
Mango Butter – 0.135
Mink Oil – 0.140
Moringa – 0.136
Myrtle oil – 0.069
Neat’s Foot Oil – 0.1359
Neem – 0.1387
Niger Seed – 0.1355
Nutmeg Butter – 0.116
Olive Oil – 0.134
Olive Butter – 0.185
Palm Kernel – 0.156
Palm – 0.141
Peanut – 0.136
Perilla – 0.1369
Pistachio Oil – 0.135
Poppy Seed Oil – 0.1383
Pork Tallow – 0.138
Pumpkin Seed – 0.1331
Ramic – 0.124
Rape Seed – 0.124
Rice Bran – 0.128
Ricinus – 0.1286
Safflower – 0.136
Sardine Oil – 0.135
Sesame Seed – 0.133
Sunflower – 0.134
Shea Butter – 0.128
Sheeps Tallow – 0.1383
Soybean – 0.135
Sunflower – 0.134
Tung – 0.1377
Veg Shortening – 0.136
Venison Fat – 0.139
Walnut – 0.1353
Wheatgerm – 0.131

I hope this helps you create some wonderful lye soap recipes, once you have success please remember to come back and post your soapmaking recipe and photos here!

Step 3: Pour into your soap mold

Soap Calculator & Formulation Guide

Select your chosen oils, along with the weight or percentage. The soap calculator will then show the total weight of lye and water required. The result can be instantly adjusted by changing your preferred superfatting level or water/lye ratio.

Discussion (22 Comments)

  1. Thanks for the knowledge shared, it’s really self explanatory and has answered a lot of questions I’ve been asking my self. thanks ????

  2. Hello, the information is insightful however, if I want to add sodium silicate and Kaolin among the ingredients, do these alter the formulations provided up?
    Thank you.

    • Hi Kiwanuka,

      Yeah, unfortunately all lye soap recipes are very sensitive to substitutions. You may need to alter the ratio of water to lye to properly saponify these new additions in a soap formulations.

  3. Hi mam,
    I just read your soap making instructions. Thank you very much. It was so easy to understand and I felt I can do it. Love ❤️
    I’ve a question here, once we make a cold process soap by making a lye and mixing it in oil and pouring in molds,
    when we take it out of mold ?
    How long soap takes to cure ?
    Can we use this cold process soap i’mmediately ?
    Can you please spare some time to answer these questions. Thanks.

    • Absolutely you can do it Arooj!

      1. Yes, but you will have to wait for the soap to solidify in the mold. This takes 24 hours, but occasionally this can take longer (especially with all olive oil soaps/castile soap).

      2. Soaps take a minimum of 4 weeks to cure, but is the same problem as above in that olive oil soaps can take as long as 6 months to a year to fully harden.

      3. No, unfortunately not, you’ll need to wait for at least 4 weeks to cure before using the soap. You can get away with using it earlier if you do a zap test, but you’ll find it will melt too quickly in the bath/shower.

      Soap making can be daunting, but you absolutely can do this! Just about anyone can make cold process soap. If you can make a meal, you can absolutely make soap! Happy soaping!

  4. This information was very useful. I am trying to add Goats milk to my soap is there a way to calculate the amount that I’m suppose to use?

    • Hi there,

      It depends on whether you’re planning to dried or fresh. If it’s fresh, you can swap like for like with your water part, or you could do 50/50 water. Whatever works for you. For the powder, you’ll need to hydrate it first, but after that, you can treat it just like fresh.

  5. Hi , This is Chandra from India. Thank you for your helpful advice .It really helped me a lot to understand the calculation of lye and water . I wanted to ask you why my cp soaps are sweating now , is it because of to much humidity. Please advice me how can I solve this problem. Thank you

    • Hi Chandra,

      It could be a number of reasons but if you send us the recipe you are using we can look into this for you.

  6. this was so helpful. I can’t wait to try my own soap recipes. thank you and bless your quality teaching heart

  7. I have been doing melt & pour for some time now, and have been too nervous to give cold process a go. All the information you have put together has made it all less confusing. Being broken down and more like bullet points didn’t stress me out so much. So much so I made my first batch last night. And look forward to un moulding and cutting tonight. And want to make my next one already. Thank you for all of your hard work and obviously your love of soaping.

  8. you are wonderful i like the way you share information .i wanna begin soap business .my interest was emancipated when i was child .

    • Hi Zewd,

      Thank you for your kind words! Starting a new craft like soap making can be so rewarding. I hope you have fun making your soaps! Any questions, let me know. 😀

  9. Thank u very much I was confused by the lye discount till I came across ur blog and now I think am good to go

  10. What can we do with the small leftover pieces of lye soap? Can we simply melt it in a stainless steel pot & then pour into a mold? There are no oils involved. It is straight lye soap from Silver Dollar City in Branson, MO. Some pieces are over 2 years old. Thank you.


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