Lye to Fat Ratio Table

This table is for those of you who want to get a bit more scientific in soap making, or just want to check and see if the person who created the recipe knew what they were doing. Each fat has its own saponification value, or "SAP Value." And because of this, each fat requires a different amount of lye to convert the fat to soap.

For the soap to be made with no left over lye or fat, you must have very accurate testing equipment. As the same oil from different sources will have a slightly different saponification value, we recommend you keep your soap a bit fat heavy to ensure you don't end up with lye in your finished product.

In the table below use the 0-4% excess fat columns (red) if you have accurate testing equipment. As the same oil from different sources will have a slightly different saponification value, we recommend you keep your soap a bit fat heavy to ensure you don't end up with lye in your finished product.

This page was written under close consultation by Tina Howard at Majestic Mountain Sage. In fact, the following table was made using her lye calculator, which will automatically calculate the amount of lye you need for a large variety of different fats.

Calculate the amount of lye you need by multiplying the amounts of each fat (including superfatting oil) in your recipe by the number intersected by the fat and your desired excess fat column. Then add the different lye amounts together.

Example: You want to calculate the amount of lye for a recipe that calls for 16 oz. (454g) of lard as its only fat. You want your finished soap to have 5% excess fat. Intersecting the Lard row with the 5% column, you find the number 0.132. Multiply 16 (fat wt) by 0.132 - 2.1 oz. (59.5 g) of lye.


NOTE: This chart is greatly expanded in Dare To Prepare


Desired Excess Fat In Finished Soap
Animal Fat
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
Goat
Lanolin
Lard
Mutton
Tallow
0.138
0.075
0.139
0.138
0.140
0.137
0.074
0.137
0.137
0.139
0.136
0.073
0.136
0.136
0.138
0.136
0.073
0.135
0.134
0.136
0.133
0.072
0.133
0.133
0.135
0.131
0.071
0.132
0.131
0.133
0.130
0.070
0.130
0.130
0.132
0.129
0.070
0.129
0.129
0.131
0.127
0.069
0.128
0.127
0.129
0.126
0.068
0.126
0.126
0.128
0.125
0.067
0.125
0.125
0.126
Vegetable Fat
0%
1%
2%
3%
4%
5%
6%
7%
8%
9% 10%
Canola Oil
Caster Oil
Coconut
Corn Oil
Cottonseed
Olive Oil
Palm Oil
Peanut Oil
Safflower
Soybean
Sunflower
0.137
0.129
0.184
0.136
0.138
0.136
0.142
0.136
0.136
0.136
0.137
0.136
0.127
0.182
0.134
0.137
0.134
0.141
0.134
0.134
0.134
0.135
0.134
0.126
0.180
0.133
0.136
0.133
0.139
0.133
0.133
0.133
0.134
0.133
0.125
0.178
0.131
0.134
0.131
0.138
0.131
0.131
0.131
0.132
0.131
0.123
0.177
0.130
0.133
0.130
0.136
0.130
0.130
0.130
0.131
0.130
0.122
0.175
0.129
0.131
0.129
0.135
0.129
0.129
0.129
0.130
0.129
0.121
0.173
0.127
0.130
0.127
0.133
0.127
0.127
0.127
0.128

0.127
0.120
0.171
0.126
0.129
0.126
0.132
0.126
0.126
0.126
0.127

0.126
0.118
0.169
0.125
0.127
0.125
0.131
0.125
0.125
0.125
0.126

0.125
0.117
0.167
0.123
0.126
0.123
0.129
0.123
0.123
0.123
0.124
0.123
0.116
0.166
0.122
0.125
0.122
0.128
0.122
0.122
0.122
0.123
Weight of water needed = Total weight
of fat in recipe times 0.38

Using potassium hydroxide instead of Lye? Lultiply the lye by 1.4. Using the example at the top of the table, 1.4 X 2.1 oz (lye used) = 2.94 oz (83.3g) of potassium hydroxide.

The superfatting columns are color-coded. The pink areas are not recommended unless the actual SAP values are known. The four green columns are most recommended and most often used. The two blue columns produce a softer soap due to the higher fat content.

All contents copyright (C) 1997-2001 Al Durtschi. All rights reserved.
This information may be used by you freely for noncommercial use with my name and E-mail address attached.

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