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Lye concentration versus Water:lye ratio

Lye Conc.,
%
Water:Lye
Ratio
Suggested usage
25 3.00 The most water in proportion to alkali (NaOH or KOH or both) that is typically used for soap. Good for making liquid soap paste, shave soap, or hot process (HP) bar soap. Not recommended for cold process (CP) soap. CP soap with this much water may not form a stable emulsion and may separate in the mold. It is very likely to be far too soft for days after saponifying.
26 2.85
27 2.70
28 2.57 Lowest lye concentration I recommend for cold process (CP) bar soap. Pros: Good for recipes high in coconut oil that can overheat and crack. May work better for complicated swirls, depending on the soaper and the recipe. Cons: Soap is more likely to gel during saponification, which you may or may not want. Soap is more likely to show streaking and mottling (aka glycerin rivers). Higher chance of emulsification failure and separation in the mold. Soap may take several days to firm up enough to be removed from the mold.
29 2.45  
30 2.33  
31 2.23
32 2.13
33 2.03 Good all-around choice for most CP recipes and many CP soap makers. Pros: Chance of gelling and "glycerin rivers" is reduced but may sometimes happen. Soap gets firmer in the mold faster. Cons: Soap may trace somewhat faster than with more water, but this is not a hard-and-fast result. The time to trace also depends on the fats and your soaping methods.
34 1.94  
35 1.86  
36 1.78
37 1.70
38 1.63
39 1.56
40 1.50 Good choice for 100% olive oil soap and other slow saponifying recipes. Pros: Chance of gelling and "glycerin rivers" is very low. Other pros and cons are same as for 33% lye concentration (2.03 water:lye ratio).
     
41 1.44  
42 1.38
43 1.33
44 1.27
45 1.22
46 1.17
47 1.13
48 1.08
49 1.04
50 1.00

A lye solution at a 50% lye concentration (1 part water to 1 part alkali by weight) contains the least amount of water in proportion to alkali that can be realistically used. If you use less water than this, not all of the alkali will dissolve. Any soap recipe can be made using a 50% lye solution, but most soapers prefer to use more water. Some soapers make a "masterbatch" lye solution using a 50% alkali concentration. Learn more about masterbatching...

 

More about Water:Lye Ratio

This ratio is the grams (or ounces) of water used for every 1 gram (or ounce) of dry alkali.

The alkali in the water:lye ratio can be NaOH or KOH or a mixture of both alkalis.

The weight units can grams or ounces or any other unit of weight. Just be consistent -- don't mix grams with ounces!

Some examples --

Water:lye ratio of 1.50 means there are 1.5 grams of water for every 1 gram of alkali.

Water:lye ratio of 2.33 means there are 2.33 grams of water for every 1 gram of alkali.

If you prefer ounces, substitute "ounce" wherever you see "gram" in these examples.

Because the lye weight is always "1," this "1" is not always shown, such as in my table (above), but sometimes the "1" is shown. For example, you might see a water:lye ratio of 1.5 that looks like these examples --

1.5:1
1.5 to 1
1.5/1

These all mean the same thing -- 1.5 parts alkali to 1 part water.

 

More about Lye Concentration

Lye concentration is the grams (or ounces) of alkali contained in 100 grams (or ounces) of lye solution.

Some examples --

Lye concentration of 33% means there are 33 grams of alkali in 100 grams of lye solution. Water makes up the rest of the 100 grams. In other words, the water weighs 100 - 33 = 67 grams.

Lye concentration of 25% means there are 25 grams of alkali in 100 grams of lye solution. The water in this solution weighs 100 - 25 = 75 grams.

If you prefer ounces, substitute "ounce" wherever you see "gram" in these examples.

As with Water:Lye ratio, the alkali can be NaOH or KOH or a mixture. The unit of weight can be ounces or grams or whatever, but you must use just one unit of weight.

 

The math behind the numbers in the table

Convert from lye concentration to water:lye ratio --

Water:Lye Ratio = 100 / Lye concentration % - 1

Example: The lye concentration is 30%. What is the water:lye ratio?
Water:Lye Ratio = 100 / 30 - 1 = 3.333333 - 1 = 2.33 (answer rounded to 2 places)

Convert from water:lye ratio to lye concentration --

Lye concentration % = Lye weight / (Lye weight + Water weight) X 100

Example: The water:lye ratio is 1.5, meaning 1.5 parts water to 1 part lye. What is the lye concentration?
Lye concentration % = 1 / (1 + 1.5) X 100 = 1 / 2.5 X 100 = 40%

 

Learn more

To learn more about choosing the right amount of water for your soap recipe, see "Full water and other drippy myths"