Concentration? Percentage? How do I figure the water amount for my lye solution?

When it comes to cold process soapmaking, some things are absolutely necessary and rigid, like how much sodium hydroxide (NaOH) is needed for a given amount of oils. It’s a property of the oils and can’t be changed without affecting the outcome of the soap, sometimes in really bad ways.

Other things are much more flexible, like the amount of water that is used to make the lye solution. The water is only there to dissolve the NaOH. Using more or less may affect how the soap mixes up, but in the end the water evaporates out and the finished, cured soap is what’s left. In fact, many experienced soapmakers use lye solutions that are quite concentrated so that they don’t have to wait so long for their bars to get dried-out and hard. It’s a real time-saver!

If you’re ready to start using your lye solution at a higher concentration, I can help you figure out how much water you will need to get there. The math can be a bit confusing for some. But I have a little formula that should do the trick.

So first, let’s explain percentage strength of a solution.

When we talk about a solution being, for example, at a 25% concentration, we are saying that it is 25% solute (the thing you are making the solution out of) and 75% diluent (the thing that you are dissolving the solute in).

In our case NaOH is the solute and water is the diluent. So a 25% lye solution is 25% NaOH and 75% water. “Per cent” means “per 100”. So the total percentage always adds up to 100.

Want another way to think about it? Imagine you have a 25% lye solution in a bowl. If you have 100 gr of lye solution in that bowl, there is 25 gr of NaOH and 75 gr of water.

OK, got the concept? Now how do you get your lye solution to be the concentration you want?

Well, you could use a lye calculator that can figure it out. The one in Soapmaker 3 software will do the math for you. So will the Soap Calc online.

But what happens when you’re not near your computer? Or you just like doing the calculations yourself. (Yay for math geeks!)

I’ll show you how to work it out. Now don’t get scared off by the math. Just think of it as a simple ratio. All we have to figure out is how many parts of water do we need for the amount of NaOH in our recipe to get a given percentage.

Here’s the formula:

(100 minus “percentage you want”) divided by “percentage you want” = the multiplication factor that you use to calculate the water

Huh? Yeah. Let’s plug in some numbers.

Let’s keep using our 25% solution example. And let’s say that I need 72g of NaOH for the recipe that I’m going to make (I used a lye calculator to figure that out for me.) I need to know how much water to use to make my solution 25%.

Here’s that formula with the numbers plugged in:

(100 minus 25) divided by 25 = 75 divided by 25 = 3.00Β  <– that is the ratio of NaOH to water

So now we multiply the amount of NaOH times the ratio:

72g X 3.00 = 216g <– the amount of water you need

Mix 72g of NaOH and 216g of water and you get 288g of a lye solution that is at 25% concentration.

Easy, right?

It works for whatever concentration you want. Just make sure your ratio answer has at least 2 decimal places to be more accurate.

Now, I’ll show you what happens if I changed my mind and I want my solution to be 34% concentration. It’s going to be more concentrated, so I’m going to need less water. How much less? Let’s find out:

(100 minus 34) divided by 34 = 66 divided by 34 = 1.94

So, 72g X 1.94 = 140 gr of water, which is what you need to make a 34% solution. Wow! That’s quite a bit less water!

Remember to use the higher concentration of NaOH only when you are comfortable with soapmaking, and are familiar with the formula that you will be using. You don’t want to do this with a brand new fragrance for example, or you may end up reading about soap that seizes!


68 thoughts on “Concentration? Percentage? How do I figure the water amount for my lye solution?

  1. Ruth thank you for spelling this out so clearly! Now even I understand! To rely on soapcalc is so easy until you don’t have it and now I don’t have to it is an option!

  2. Hi Ruth, I attended my first HSMG conference last week and heard you speak on alternative liquids. Thanks so much for sharing your knowledge. You are a good speaker, I like how simple you make it. I’d like to try this method, does it shorten curing times at all? For a first timer how much of a solution would you suggest? I am currently using a 28% solution (if I did the math right).


    • Hi Naomi! I’m glad you enjoyed my talk!
      Yes, using less water to make your lye solution does mean that your soap will be dryer sooner. So it will probably cut a week or so from curing time, depending on where you live. For a beginner, 28% is a great concentration. Once you get comfortable with soapmaking, and are familiar with making a few batches with a given fragrance, then you can try 30% or 33%. The highest I’ve ever heard of using is 40%, but that was from some very experienced soapmakers!
      Good luck with yours!

  3. Ruth, I just wanted to give you a quick update. I tried using 34% lye solution and I’m thrilled with the results! Thanks so much again for sharing this information. I found my soap is drier much sooner than usual. I found I can cut 24 hours off my waiting time before cutting my soap. I used to wait until my soap is 4 weeks old to stamp it because it was so soft, but now I am able to cut that down to just 2 weeks. In addition to that I’ve cut one whole week off of my curing time, yah! I’ve discovered that I must work even quicker with certain FOs that are prone to seizing, though. I’ve made 15 small batches with this new formula and I’m making it a permanent change. Many thanks to you!

  4. Ruth thank u for yuors willingness .i tried to make with 28% concentration but i have not understand how much fatty acid used for 72 gm of NaOH ? And when i tried 500gm fatty the lather of soap is not enough so what shall i do for better lather formation thank u for yours time spending

  5. How can I make my bar soap harder and prevent it from sweating. I’m in Ghana can u assist me to get get titanium dioxide 1kg to buy? Can you help me get it through post since i can get here, by letting me know mode of payment?

    • Hi! Are you asking about cold process soap? Oils that help with making a harder bar are palm oil, cocoa butter and rice bran oil. Try including some of those in your recipe. The sweating comes from the glycerin in the soap. Depending on your environment and how humid the air is, it may be hard to stop that. Try storing the soap in as dry a place as you can. And I don’t sell supplies, but some of my favorite US suppliers are Bramble Berry, TKB Trading and Soap Making Resource. Good luck!

  6. Great article Ruth – I’m not sure what I was doing during maths at high school, but it wasn’t maths. My burning question is this. I’m upscaling the size of my batches so the slushy method of goat milk soap making is getting harder to manage. I want to make a very concentrated lye and then use goat milk to make the balance. I’ve always made 100% goat milk so I’m not keen on going to 50/50 style. I’d like to know how concentrated a lye solution I can make without the sodium hydroxide saturating the solution and precipitating.

    • Thanks, Melissa. I’m afraid that the highest concentration you can go with sodium hydroxide is 50% before it just won’t go into solution anymore. So that means 50% goat milk is the best you can do, unless you use evaporated goat milk. But I’m guessing that you have your own fresh goat milk, so that wouldn’t be very appealing to you. But I think 50% goat milk is still pretty wonderful! πŸ™‚

  7. I have been making soap for 3 years using the water to oil % and have just learned about the lye concentration, dont know how i missed it before. I’ve been using 38% water to oils, so if i change to using the lye concentration method ( I understand how to work it out I’m not sure what concentration i should use. I have been playing around with soapcalc and notice that the amount of water changes with the oils used so it seems that this is a better method as its targeted more to the oils you are using but I’m still unsure what concentration to start at. I thought that 38% water to oils was a bit much but i noticed that if i did a 100% coconut oil soap using 30% lye concebtration the water works out to be 40.619 % to oils, so I guess I’m still a little confused.

    • Hi Kerrie,
      Funny: I’m just the opposite. I’ve never used the water to oil % to calculate the water, only lye concentration. The water amount changes with a change in oils because it’s based on the amount of sodium hydroxide. So if you change the oils, that will change the amount of sodium hydroxide you need, and that will change the amount of water you need if you are going to have the same concentration. I like to use 29% lye solution in general. It’s great when I’m using new fragrances (that might seize or accelerate trace) and gives me plenty of time to do swirling techniques. But for recipes that I am familiar with and don’t need to stay at a thin trace, you can go up to 30-33%. Experienced soapmakers even go up at high as 35-40%. The higher the concentration, the less water, and the sooner your bars will be dry (since they have less water that needs to evaporate out). Soapmaking can be very flexible, so just use what works for you!

  8. Thank you ruth, your article surely educated to me about lye, lye solution and water. But I still have question that is lye used in hot process? and is there any difference between hot process & melt and pour process?

    • I’m glad you found it helpful, Wajid. Yes, lye is still necessary for hot process soapmaking. The only difference between hot process and cold process is that you heat up the soap mixture before putting it in the mold. That way you speed up the process and saponification is complete before pouring. Melt and pour soap is ready-to-use soap that is meltable so that you can add color and scent to it. No lye is needed because it has already been turned into soap.

  9. Hi I am new here, my Q is as per your explanations in the earlier post, to make a 50% concentration of NaOH solution, i should add 500gm of pellets and 500 ml of water. Is this correct.
    I also need to know , if i heat this liquid to (1) 100 deg C or (2) 160 deg C what will happen.
    Will the concentration change due to loss of water vapour.
    What would be the max recommended temp that i could heat the Naoh of 50% conc too.
    I tried ot find answers all over the internet , but i have got more confused.

    • Rajiv, yes, to make a 50% solution you would mix equal amounts of water and sodium hydroxide. But there is no need to heat lye solution. Even if it gets cool, you can still use it as is. Lye solution does not need to be warm to work. I hope that helps answer your question!

  10. Thanks Ruth, What troubles me , if when i start with say 100 gm of NaOH pellets and 100 gm ( 100 Ml) of water, will i get 100 ml of lye or will the volume /wt increase.

    • Mass (or weight) never disappears. So if you mix 100gm NaOH with 100gm (remember to also weigh your water) of water, you will have a solution that weighs 200gm. Now, in reality some of that water will evaporate as the solution cools. A surprising amount actually. You can weigh it yourself after it cools and see the difference. I recommend when you are making a 50% solution to weigh your solution and replace the evaporated water with more fresh water. In other words, right before using it, weigh the solution and add enough water to bring it back up to 200gm.

  11. Thanks Ruth, this is very helpful.
    I plan to leach some SiO2 with NaOH, do I need to heat the reactants for them to react.Pls advise.

  12. Hi Ruth, is it still possible to make cold process soap with a 16% lye solution? E.g 160 gram of sodium hydroxide and 840 gram of distilled water? Thank you for your article, I tried calculating using soap calc and understand that a change in the lye concentration (e.g. 16%) does not affect the amount of actual lye computed to saponify oil and it only changes the amount of water ratio. But would a lye solution of 16% be too much water? Would it take many days to cure? now that the total soap weight is much larger with more than normal amount of water, would the soap cure and become much smaller than the mold? I am working on such a low concentration because I’m only able to get a lye solution maximum at 16% in my country. Appreciate your advice please.

    • Hi Raymond! While it IS possible to make soap with a solution that is 16%, I’ve never done that before. And my concern is that with so much water, it may take a lot of blending to get the mixture to trace, and it may be weeks before the soap is ready to cut. If you have no other choice, then maybe hot process might be a better technique for you. That way some of the water would evaporate off during the cooking stage, and the soap would be dry sooner. While I’ve used the hot process a few times, I’m no expert. If you are looking for instruction, The Nova Studio has a great class handout for sale. But I teach there, so I’m biased. πŸ˜‰

  13. Thanks Ruth. I am a beginner in soap making and your article solved the problem of making lye solution . Is there any ratio of amount of oils to lye solution to be used?

  14. IN Arabia we grown up with decimal system
    a simpler way solving your example is:

    for 1st example:

    You stated 72g and 25% so:
    72 / 0.25 = 288 total volume
    288-72=216 water

    for the 2nd example:
    72/0.34=211.76 total volume
    211.76-72 =139.76 water

    good luck

    • “Passing by”, you are absolutely right. And many soapmakers that I’ve met like to think of their lye solution in ratio to water, so I wanted to give them a way figure ratios for any percentage. Cheers!

  15. I have recently used Soap Calc to run a recipe with a tiny change in oil as I wanted to use a small amount of Almond Oil to mix my color in and it made Soap Calc turn out like this below. The Water:Lye Ratio shows 787:1 which is confusing me.

    The only thing I changed on the recipe is the addition of 10 grams of Almond Oil. The original recipe called for no Almond oil and it gave me a Water :Lye Ratio of 1.3364 :1 which sounds accurate.

    Should I be worried? It seems to have thickened up well and is just in the gel stage now.

    SoapCalc Β© Recipe Name: New Print Recipe

    Total oil weight 2373 g
    Water as percent of oil weight 36.20 %
    Super Fat/Discount 5 %
    Lye Concentration 29.982 %
    Water : Lye Ratio 787.0000:1

    Sat : Unsat Ratio 40 : 60
    Iodine 61
    INS 168
    Fragrance Ratio 25
    Fragrance Weight 59.33 g

    Pounds Ounces Grams
    Water 1.894 30.31 859.14
    Lye – NaOH 0.811 12.98 367.89
    Oils 5.232 83.71 2,373.00
    Fragrance 0.131 2.09 59.33
    Soap weight before CP cure or HP cookMore info 8.068 129.08 3,659.36

    # √ Oil/Fat % Pounds Ounces Grams
    1 Almond Oil, sweet 0.42 0.022 0.35 10.00
    2 Olive Oil 70.80 3.704 59.26 1,680.00
    3 Coconut Oil, fractionated 28.78 1.506 24.09 683.00
    Totals 100.00 5.232 83.71 2,373.00

    Soap Bar Quality Range Your Recipe
    Hardness 29 – 54 41
    Cleansing 12 – 22 29
    Conditioning 44 – 69 58
    Bubbly 14 – 46 29
    Creamy 16 – 48 12
    Iodine 41 – 70 61
    INS 136 – 165 168

    Lauric 1
    Myristic 0
    Palmitic 10
    Stearic 2
    Ricinoleic 0
    Oleic 49
    Linoleic 9
    Linolenic 1

    Hard Cleansing Conditioning Bubbly Creamy

  16. Hi Jacqueline, I’m not sure what happened with the lye calculator and the water ratio. But did you mean to include fractionated coconut oil? Could that be part of the problem. I’ve never made soap with that, so I’m not sure how it would turn out.

  17. if i have 50% NaOH soln of 1000 litre and i want to make it 30% NaOH soln then how much water i need to add?

    thank you

    • Rahul, in your 1000 liter solution you have 500kg of NaOH (since it’s 50% solution). To make a 30% solution of 500kg of NaOH, you would need 1166kg of water. Since your 1000 liter of 50% solution already has 500kg of water, you need to add another 667kg of water for a total of 1667kg of 30% solution. That’s a lot of lye! πŸ™‚

  18. ruth im new on this want to start up soap making,i m totally new
    please give me ur link for beginers i will appreciate,cos i dont adequate percentage for the chemicals
    like how to calculate oil% and lye,i only learnt water thanks to you

  19. Thank you for the explanation. But I find one info missing.
    Where does this 28% concentration come from? I mean, what is the reason for deciding to use 28% and not 38%? How do I decide what percentage to use? You said experienced soap makers use higher percentage – but on another site I actually read that experienced soap makers use lower.
    So what’s the deal with the percentage?

    • Hi Gabor, thanks for asking a great question! The higher the % concentration, the less water there is to dilute your sodium hydroxide and oils. This generally will lead to the saponification reaction starting more quickly (because the molecules are closer together). With less water, there’s the possibility that your soap may become so thick in the pot that it is hard to pour. That’s why we suggest that you use a higher concentration solution only when you are experienced with your recipe. Perhaps that other site meant that experienced soapmakers use less water in their recipe; that would result in a higher concentration of lye also. Sometimes, even experienced soapmakers will use a lower concentration lye solution if s/he wants the soap batter to be very fluid for making a certain pattern or swirl. The lower the concentration, the more water, and the longer the batter will stay thin enough to pour and manipulate. Soapmakers have lots of options!

  20. Hi dear Ruth! May I ask you something? I bought a 50% NaOH solution. So this means that 1000 grams solution contains 500 grams NaOH. But I read in a data sheet of another NaOH that 50% NaOH solution contains 764.780 grams/L. This means volume not weght right? So how can find NaOH content in grams / Kg?

    • Scott, I’m sorry that I don’t have more experience with purchasing 50% solutions of NaOH. Since 1L of water weighs 1Kg, I’m also confused by the 764.780 gram/L. If I were you, I would contact the manufacturer and ask that they clarify that for you. Sorry I couldn’t be more helpful!

  21. What is the difference between a shampoo bar and a body bar? Is there a different formula for making shampoo bars? Thanks!

  22. Can I use 50 percent of my water to dilute lye; Use the other 50 percent to prepare Concentrated goat milk and freeze it; and finally. add the iced concentrated goat milk to the concentrated lue solution?

    I ask because I mixed lye with goat milk ice cubes to make soap. Unfortunately, my soap had crystals on lye that didn’t dilute.

    • Sandra, yes you can do that. The only limitation is that you have to use at least the same amount of water as sodium hydroxide to make your lye solution. Otherwise all of the sodium hydroxide won’t dissolve. I’ve had the same experience in the past with bits of sodium hydroxide in my milk soaps. I found that if I stirred the milk and sodium hydroxide a bit longer, letting the mixture get a bit warmer, it avoided that problem. It takes longer for the sodium hydroxide to dissolve in the low temperature of the frozen milk.

  23. Dear Sir. Madam
    thanks alot for all information given at your website really it was helpful and more useful special for the beginners .
    We shall be grateful if you could inform us the ideal percentage of Sodium Hydroxide used for Saponification ?
    Is the percentage of the lay depending on what? For example the percentage of liquid oil and super fat or what factor?
    Your earlier reply will be highly appreciated.
    Best regards
    Mohammed Shawki

  24. Hi,
    I would like to have the possibility to introduce a SOAP CALCULATOR that I developed in the last years…
    I always found a lot of Soap Calculators on the web, but I never found one able to calculate the % of Glycerin inside the final soap, because mixing oils and caustic soda, the reaction produce not olny soap, but also glycerin. So some times ago I decived to developed a special soap calculator.
    I would like to invite all the users to try it and let me know your comments.
    The calculator is here:
    Bye !

  25. Thank you for finally making some sense of this topic for me!! During the 18 months since I started, I’ve been using soapcalc to play with my recipes and could not understand why the ‘water as percent of oils’ feature didn’t work as I thought it should. Now, after reading your response to Kerrie Kelly above, I see that I’ve been confusing my understanding of lye concentration with what that feature is meant for.

    I’ve now bookmarked your page to come back to when I need clear-cut answers or just want to learn something new.

    Thanks so much, Ruth!

    Be Blessed!

  26. When using %w/w in creating an oil based solution, how does one come up with how much oil to use since 1ml doesn’t equal 1gr except for water of course.

    • Hi Todd, when designing a soap recipe, you want to calculate always by weight. So it doesn’t matter what the specific gravity of an oil is (whether 1 ml of the oil weighs 1 gr) because we never use volume to measure oils (or water, for that matter).

      • So if the protocol has it at 0.05% of frankensense oil, how much oil will I use in 100grams total weight? 0.05ml? If that’s the answer, wouldn’t that say that 1gr = 1 ml. Trying to understand:)

      • how would you measure 2 grams or which ever is needed? Is your method weighing the oil (liquid) or using density in formula? thanks for the help

      • Todd, if you want to add the oil at 0.05% and you are using 100 grams total, then you will add 0.05 grams of that oil. If you want an oil to be 2% of your total and you have 100 grams total, then you will add 2 grams of that oil. The other 98 grams will be all the other oils.

      • Todd, I weigh everything with a digital scale. The only ingredients I don’t weigh are my powder colorants, like oxides and micas. Those are not involved in the saponification reaction, so it’s less critical to be accurate with them.

  27. I grow sunflower in large scale and do make sunflower oil.
    How can i make hard and lather bar soap using only sunflower oil and lye?Please provide a formulae of mixing a litre of sunflower oil,water and lye to come up with a good soap.

    • A soap that is 100% sunflower oil is not going to make a hard bar, nor will it lather much.It will be very moisturising though.You should learn how to use SoapCalc and learn the properties of oils. You will have to use a big water discount. also this batch could go rancid.

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