Definition: Reichert–Meissl number is defined as the number of 0.1 N KOH required to completely neutralise the soluble volatile fatty acids distilled from 5 gm of fat.

Example:   Butter:    25–30

Significance: RM number is useful in testing the purity of butter since it contains a good concentration of volatile fatty acids. Butter has RM number in the range of 25–30 while it is less than 1 for most other edible oils. Thus any adulteration of butter can be easily tested by this RM value.