Air Quality Improvement: Filtration removes up to 99.97% of airborne particles as small as 0.3 microns in size including smoke, dust, pollen, pet dander, mold spores and dust mite debris Maintenance: Recommended to replacement filter every twelve (12) months and pre-filter every three (3) months for maximum efficiency, or more often in harsh environments. Approximate Dimensions: Filter - 16 x 11 x 2 inches Pre-Filter - 16 1/4 x 11 3/4 x 1/8 inches What You Get: One (1) replacement filter and four (4) replacement pre-filters. Approximate Dimensions: 16 x 11 x 2 inches Filter-Monster branded replacement filters compatible with Whirlpool Small Air Purifier includes one (1) filter and four (4) carbon pre-filters.