Saponification Value Calculator

Saponification value (SV), also called SAP value, is the number of milligrams of potassium hydroxide (KOH) required to fully saponify (convert to soap) 1 gram of a specific fat or oil. It is calculated as SV = (56,100 x n) / MW, where MW is the average molecular weight of the fat and n is the number of saponifiable ester groups per molecule, commonly 3 for a triglyceride.

Use SV = (56,100 x n) / MW. The constant 56,100 is the molar mass of KOH (56.1 g/mol) expressed in mg/mol, and n is the number of ester groups reacting per molecule (3 for a standard triglyceride fat or oil). For an oil with average molecular weight 872 g/mol, SV = (56,100 x 3) / 872 = 193.0 mg KOH/g.

Multiply the oil mass by the oil's saponification value, then divide by 1000 to convert from milligrams to grams: KOH(g) = oil mass(g) x SV / 1000. For 500 g of an oil with SV 190, KOH needed = 500 x 190 / 1000 = 95 g before any superfat discount.

Superfatting means deliberately using slightly less lye than the exact amount needed to saponify all the fat in a recipe, so a small percentage of unreacted oil remains in the finished bar. This improves mildness and moisturizing feel. A common superfat range is 3-8%; this calculator applies it as a percentage discount off the stoichiometric KOH amount.

The stoichiometric KOH amount (0% superfat) is multiplied by (1 - superfat / 100). For example, with a stoichiometric requirement of 95 g KOH and a 5% superfat, actual KOH used = 95 x (1 - 0.05) = 90.25 g, leaving the remaining fat unreacted in the soap.

56,100 comes from the molar mass of potassium hydroxide (56.1 g/mol) expressed in milligrams per mole (56.1 x 1000 = 56,100). Saponification value is conventionally expressed in mg KOH per gram of fat, so this constant converts moles of KOH required per mole of fat into the mg-per-gram scale used in SV tables.

n is the number of saponifiable ester bonds per molecule of fat that react with KOH during saponification. A standard triglyceride (the form of most vegetable and animal fats) has 3 fatty acid chains attached to a glycerol backbone, so n = 3 for the vast majority of soap-making oils. Some specialty esters or waxes may have a different n.

Yes. Enter your oil mass and SV to get the KOH requirement, and the calculator also reports the equivalent NaOH mass, calculated using the ratio of NaOH's molar mass (39.997 g/mol) to KOH's molar mass (56.106 g/mol). KOH is typically used for liquid soap, while NaOH is typically used for solid bar soap.

Yes, significantly. Saponification value depends on the average molecular weight of the fat's fatty acid chains: shorter-chain, lower molecular weight oils like coconut oil have higher SV values (more ester groups per gram), while longer-chain, higher molecular weight oils like olive oil have lower SV values. Always use the specific oil's published SV rather than assuming one value fits all oils.

No, they measure different properties. Saponification value measures how much KOH is needed to saponify a fat and is used to calculate lye amounts. Iodine value measures the degree of unsaturation (number of double bonds) in the fatty acids and relates to how hard or soft the resulting soap will be. Both are useful reference numbers for formulating soap but answer different questions.

Too little lye (heavy superfat, or an error toward less KOH/NaOH) leaves excess unreacted oil, which can make soap soft, greasy, or prone to rancidity if pushed too far. Too much lye (not enough superfat, or an error toward more KOH/NaOH) can leave the soap caustic and harsh on skin. Careful, accurate calculation of the lye amount for your specific oils and desired superfat is one of the most important steps in safe soap making.