HEPA filters

A high-efficiency particulate air (HEPA) filter can remove 99.97% - 99.99% of airborne particles that are equal to, smaller or larger than 0.3 microns in size The efficiency is rated based on the worst level possible, so think about it as 99.97% or BETTER.

HEPA filters are tested using air particles that are 0.3 micron size as those are the most difficult size for a HEPA filter to catch. HEPA filters are actually more efficient at capturing smaller-sized particles, like those the size of viruses (which on average are 0.1 microns)