What this calculator does
Saponification value is the milligrams of potassium hydroxide needed to saponify one gram of fat. It is measured by refluxing the sample with excess KOH and back-titrating what remains against the same treatment without a sample.
The figure is inversely related to the average chain length of the fatty acids. Short chains mean more ester groups per gram and therefore more KOH consumed, so coconut oil sits around 255 while olive oil is nearer 190. A low value indicates long chains.
The formula
The difference between the blank and sample titration volumes gives the acid that did not react with leftover KOH, which equals the KOH the fat consumed. Multiplying by the acid molarity and by 56.1, the molar mass of KOH, converts moles to milligrams, and dividing by the sample weight gives the value per gram.
| Term | Meaning |
|---|---|
| Saponification value | Milligrams of KOH per gram of fat. |
| Back-titration | Adding a known excess and titrating what remains, used when the direct reaction is slow. |
| Blank | The same procedure without sample, establishing how much KOH was present to start with. |
| Chain length | The main determinant of the value, since shorter chains mean more ester groups per gram. |
The inputs explained
| Field | What to enter |
|---|---|
| Blank titration volume (mL) | Blank titration volume: acid used with no sample present. |
| Sample titration volume (mL) | Sample titration volume: acid used with the sample. Always less than the blank. |
| Molarity of HCl (mol/L) | Molarity of the hydrochloric acid used for the titration. |
| Sample weight (g) | Sample weight in grams. |
When to use it
Soap making
The value determines how much alkali a given oil needs, which is essential for formulating a soap that is neither harsh nor greasy.
Characterising an oil
The value helps identify an oil and detect adulteration, since each has a characteristic range.
Quality control
A value outside the expected range for a named oil indicates contamination or mislabelling.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does the titration difference affect the value?
A range of sample titration volumes.
| Sample titration volume | Saponification value | Volume difference | Sample weight used |
|---|---|---|---|
| 18 mL | 98.18 mg KOH/g | 7.00 mL | 2.000 g |
| 20 mL | 70.13 mg KOH/g | 5.00 mL | 2.000 g |
| 22 mL | 42.08 mg KOH/g | 3.00 mL | 2.000 g |
| 24 mL | 14.03 mg KOH/g | 1.00 mL | 2.000 g |
Questions
What is a typical saponification value?
Around 190 for olive oil, 195 for palm oil and 255 for coconut oil. Shorter fatty acid chains give higher values because a gram of them contains more ester groups. A value well outside the expected range for a named oil suggests adulteration.
Why use a back-titration?
Because saponification is slow and needs prolonged refluxing, so titrating directly against the fat is impractical. Adding a known excess of KOH, letting it react to completion, and titrating the remainder is both faster and more accurate.
What is the blank for?
To establish exactly how much KOH was added, since the stock concentration may drift and the exact volume delivered varies. Running the identical procedure without sample and titrating gives the starting point the sample result is measured against.
How does this relate to soap making?
Directly. The value tells you how much alkali each oil needs. Soap recipes use it to calculate the lye required, usually with a small deficit so that a little unreacted oil remains and the soap is not harsh. Sodium hydroxide recipes scale the KOH figure by the molar mass ratio.
For finding a concentration by titration, see the titration calculator. For protein estimation from another indirect measurement, see the crude protein calculator.