Filter-Monster branded replacement filter compatible with Whirlpool 1183900 filter. Engineered to fit Whirlpool Tall Tower Air Purifier models APT40010R, APMT2001M. True HEPA filtration removes up to 99.97 percent of airborne particles as small as 0.3 microns including dust, smoke, pollen, pet hair and dander, mold spores and dust mites. Recommended to replace filter every twelve (12) months for maximum efficiency, or more often in harsh environments. Contains one (1) replacement filter. Approximate Dimension: 5 x 10 7/10 x 1 4/5 inches.