# Saponification overview of oil SAP values

Our saponification values come primarily from our suppliers and product documentation. In some cases, we have relied on outside sources. Some GSP values will differ from those reported in other sources because GSP values may fall within a range of values that are acceptable for an oil/butter/lipid. The actual value will change depending on the origin of the lipid and what the weather conditions were for that particular plant material and processing techniques. In most cases, we used an average of the range so that your soap does not become leach heavy in case the actual GSP value was at the lower end of the range.

These numbers are actual SAP values expressed as the number of mg of KOH required to saponify 1 g of oil/fat. When reading a certificate of analysis of an oil/fat, the SAP Value is indicated in this way.

Most soap makers prefer to convert these numbers when making soap to easily calculate their lye. You see these converted values as decimal values. They are derived from the actual GSP value and are not true GSP values.

Dividing the SAP value by 1000 gives us a ratio of KOH to oil in the same units (mg), and therefore becomes the ratio of KOH needed for each unit as long as you use the same units to measure your KOH and oils. Example: An oil with an average SAP value of 190 needs 190/1000 = 0.190 g KOH per g of oil, or 0.190 ounces of KOH per ounce of oil, or 0.190 pounds of KOH per pound of oil.

Dividing the SAP value by 1402.50 or multiplying the KOH ratio by 40/56.1 (the ratio of the molecular weights of NaOH/KOH), gives us the amount of NaOH needed for each unit, as long as you use the same units for NaOH and oils. Example: An oil with an average SAP value of 190 requires 190/1402.50 = 0.135 g of NaOH per 1 g of oil, 0.135 ounces of NaOH per ounce of oil or 0.135 pounds of NaOH per pound of oil.

Summary:
To convert actual SAP values into converted values ready to work with in any unit:

Solid soap (NaOH): divide the average SAP value by 1402.50
Liquid soap (KOH): divide the average SAP value by 1000

## Soap recipe calculation

With these known values, a calculation can now be made. If the saponification number has a staggered value then the average is used in the calculation. Practice will show if this number needs to be adjusted, if the soap is too fatty the average saponification value must be adjusted up and if the soap contains too little fat the average value will have to be lowered.

Lye calculation example hard soap:

• Olive oil 184-196, average 190, quantity 100 grams
• Coconut oil 250-264, average 257, quantity 100 grams
• Leaching strength 27% NaOH
• Overfat 1%

Formula lye: (saponification / 1422.9803) x ((grams of oil / 100) x (100 – overfatting)) = grams of NaOH

Lye calculation:

• Olive oil: (190 / 1422.9803) x ((100 / 100) x (100 – 1)) = 13.219 grams of NaOH
• Coconut oil: (257 / 1422.9803) x ((100 / 100) x (100 – 1)) = 17.882 grams of NaOH
• Total: 31.173 grams of NaOH

Now that the amount of lye is known, the amount of water can be calculated.
Formula water: (grams of NaOH / lye strength) x 100 – grams of Naoh = grams of water

Lye calculation:
Olive oil: (13.219 / 27) x 100 – 13.219 = 35.741 grams of water

Coconut oil: (17.882 / 27) x 100 – 17.882 = 48.346 grams of water

Total: 84.087 grams of water

To make hard soap from 100 grams of olive oil and 100 grams of coconut oil requires 31.173 grams of NaOH dissolved in 84.087 grams of water. By using two types of oils, the calculated quantities must be added together and soap making can be started. For liquid soap, KOH is used, the lye strength is around 20%. The hardness of the water neutralizes a small amount of lye because of this the overfatting of the soap will increase. Distilled water does not affect leach strength.