Micronrating

Micronrating is a specification used for filtration products to describe the intended size of particles that the device can remove from a fluid or gas, expressed in micrometers (µm). A micron is one millionth of a meter. The rating provides a rough sense of how fine the filtration is—for example, a 5 µm filter is expected to capture some particles around five micrometers in size or larger, though performance depends on flow and other conditions.

Filtration ratings are commonly described as nominal or absolute. Nominal ratings indicate an approximate level of filtration, with a substantial fraction of particles larger than the rated size being captured, but smaller particles may pass. Absolute ratings imply a tighter, more predictable level of filtration, closer to the stated pore size, but true performance still depends on testing conditions.

Micron ratings are determined under laboratory conditions using standardized test particles, and different manufacturers may use different test methods. For drinking water and home-use filters, micron ratings are often used alongside standards from organizations such as NSF/ANSI; for air filters, manufacturers may report micron size ranges for captured particulates, but consumer clarity varies because air filtration is also described by other metrics such as particle counts and efficiency at specific sizes.

Users should view micron ratings as an indicator rather than a guarantee. Real-world performance is affected by flow rate, pressure drop, filter age, dirt loading, and the distribution of particle sizes. When selecting a filter, consider the rated micron size in combination with independent test results, replacement schedules, and the intended application.