A filter, cartridge or mask's rating tells you what and how much particles are actually being filtered. Below is a list of a respirator rating letters and numbers, and what they mean:
- N: The letter "N" represents a mask or filter that is not resistant to oil-based particles.
- R: The letter "R" represents a mask or filter that is resistant to oil-based particles.
- P: The letter "P" represents a mask or filter that is oil proof.
- 95: A rating of 95 means it removes 95% of all particles that are at least 0.3 microns in diameter.
- 99: A rating of 99 means it removes 99% of all particles that are at least 0.3 microns in diameter.
- 100: A rating of 100 means it removes 99.97% of all particles that are at least 0.3 microns in diameter or larger. This is considered "HE" or "HEPA" quality, because it's considered "High Efficiency".
- P2 (European Standard): Filters at least 94% of airborne particles (Similar to P95)
- P3 (European Standard): Filters at least 99.95% of airborne particles (Similar to P100)