The filter industry is in a state of confusion about rating their filters. Customers want a simple way to compare filter elements so the micron ratings system was invented. A micron rating is an arbitrary value assigned to a filter by the manufacturer, not an actual measured value. It quotes a particle size without establishing the filter’s efficiency at removing that size particle.

Since the micron rating cannot be verified, filter manufacturers feel safe in assigning any number that they want. It is not recommended to use micron ratings to compare filter elements.