The Acid Value Calculator determines the milligrams of KOH required to neutralize free fatty acids in one gram of fat or oil. Used in food science, biodiesel production, and quality control to assess oil freshness, hydrolytic rancidity, and refining requirements.
5.83
mg KOH/g
2.93
%
2.08
%
2.66
%
5.83
mg KOH/g
2.93
%
2.08
%
2.66
%
The calculator for acid value (AV) computes the number of milligrams of potassium hydroxide (KOH) required to neutralize the free fatty acids (FFA) present in one gram of fat, oil, or lipid sample. Acid value is the primary quality indicator for fats and oils in food science, oleochemistry, and biodiesel production — it quantifies the degree of hydrolytic degradation that has occurred since the oil was produced or refined.
Acid value is determined by titrating a dissolved oil sample with standardized KOH solution:
AV = (V × N × 56.11) / m
where V is the volume of KOH solution used (mL), N is the normality of the KOH solution (mol/L), 56.11 is the molecular weight of KOH (g/mol), and m is the mass of the oil sample (g). The factor 56.11 converts moles of KOH to milligrams, giving the final result in mg KOH/g oil. The saponification value calculator measures total fatty acid content (both free and esterified), while acid value measures only the free fraction.
Acid value is often reported as Free Fatty Acid percentage referenced to a specific fatty acid. The conversion depends on which fatty acid is used as the reference:
The choice of reference fatty acid reflects the predominant fatty acid in each oil type. Comparing FFA% values across different oils is only meaningful if the same reference is used. Use this online calculator to convert between AV and FFA% for any reference fatty acid. The iodine value calculator and organic reactions calculators category cover complementary oil quality parameters.
Industry standards define maximum acceptable acid values across different uses:
High acid values indicate hydrolytic rancidity caused by moisture, heat, microbial lipase activity, or prolonged storage. Refining processes (neutralization with alkali) reduce AV but remove beneficial minor components. The ester value calculator and hydroxyl value calculator complete the standard oil characterization panel.
The acid value determination is a direct titration of free fatty acids with standard KOH solution:
$$R\text{-}COOH + KOH \rightarrow R\text{-}COOK + H_2O$$
The acid value is calculated as:
$$AV = \frac{V \times N \times 56.1}{W}$$
where $$V$$ is the volume of KOH solution used (mL), $$N$$ is the normality of KOH, 56.1 is the molecular weight of KOH (g/mol), and $$W$$ is the sample weight (g).
The free fatty acid percentage is related to the acid value by the fatty acid molecular weight:
$$\%FFA = \frac{V \times N \times MW_{FA}/2}{W}$$
Common conversion factors: as oleic acid (MW 282.5, factor = 28.2), as lauric acid (MW 200.3, factor = 20.0), as palmitic acid (MW 256.4, factor = 25.6). Oleic acid is used for most vegetable oils, lauric acid for coconut and palm kernel oils, and palmitic acid for palm oil.
For refined edible oils, acid value should be below 0.6 mg KOH/g (corresponding to ~0.3% FFA as oleic). Virgin olive oil allows up to 1.6 mg KOH/g (0.8% FFA). Crude oils before refining may have AV of 2-10 mg KOH/g. Values above 4 mg KOH/g generally indicate significant hydrolytic degradation. For biodiesel feedstock, acid value must be below 1 mg KOH/g to prevent soap formation during transesterification. In soap manufacturing, a high acid value in the starting fat means more free acid is already present, slightly reducing the KOH needed for saponification. The choice of FFA expression (oleic vs lauric vs palmitic) should match the predominant fatty acid in the oil being tested.
Inputs
Results
AV = (0.8 × 0.1 × 56.1)/10.0 = 0.45 mg KOH/g. Below 0.6 — acceptable for refined edible oil.
Inputs
Results
AV = (5.2 × 0.1 × 56.1)/5.0 = 5.83 mg KOH/g. High acid value indicates significant hydrolytic rancidity.
The acid value (also called acid number) is the mass of KOH in milligrams required to neutralize the free fatty acids in one gram of a fat or oil sample. It measures the extent of triglyceride hydrolysis and is an indicator of oil quality, freshness, and degree of degradation.
High acid values result from hydrolysis of triglycerides into free fatty acids and glycerol. This is caused by moisture, high temperature, lipase enzymes (from seeds or microbial contamination), prolonged storage, or exposure to metals that catalyze degradation.
They measure the same thing differently. Acid value is in mg KOH/g (absolute amount of base needed). FFA% expresses the result as a weight percentage of a reference fatty acid. To convert: FFA% (as oleic) = AV × 0.503. They are interchangeable with the appropriate conversion factor.
The FFA% depends on the assumed fatty acid molecular weight. Oleic acid (C18:1, MW 282) is used for most vegetable oils where C18 fatty acids predominate. Lauric acid (C12:0, MW 200) is used for coconut and palm kernel oils. Palmitic acid (C16:0, MW 256) is used for palm oil.
Codex Alimentarius standards specify: refined oils ≤ 0.6 mg KOH/g, cold-pressed oils ≤ 4.0 mg KOH/g, virgin olive oil ≤ 1.6 mg KOH/g (extra virgin ≤ 0.8 mg KOH/g). Values above these limits indicate the oil is not fit for the labeled grade.
High FFA content (AV > 1 mg KOH/g) causes soap formation during base-catalyzed transesterification, reducing biodiesel yield and complicating separation. Oils with high AV require either acid pre-esterification of the FFA or acid-catalyzed transesterification instead.
Yes. Frying accelerates hydrolysis due to high temperature and moisture from food. Many countries regulate that frying oil must be discarded when the acid value exceeds certain limits (typically 2-4 mg KOH/g) to protect consumer health.
Acid value measures hydrolytic rancidity (free fatty acid formation), while peroxide value measures oxidative rancidity (peroxide formation from double bond oxidation). They measure different degradation pathways. An oil can have high AV but low PV (hydrolysis without oxidation), or vice versa.
Phenolphthalein is the standard indicator, changing from colorless to pink at pH ~8.2. The sample is dissolved in a warm ethanol-diethyl ether mixture (1:1) to ensure homogeneous solution, and the titration proceeds until a faint persistent pink color appears.
Yes. The refining process includes a neutralization step (degumming and alkali refining) where free fatty acids are converted to soapstock by treatment with NaOH. This removes FFA and reduces the acid value to the low levels required for edible oil standards.
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