Compatibility: Compatible with Blueair 411 particle and carbon filter. Fits Blueair Pure 411, 411+, 411 Auto, and 411 Mini air purifiers. Air Quality Improvement: Filtration is rated H13 and removes up to 99.97% of airborne particles as small as 0.3 microns in size including dust, smoke, pollen, pet hair and dander, and more. Maintenance: Recommended to change this filter once every six (6) months under normal conditions, and more often under harsh air conditions. Replacement Quantity: Each package contains one (1) replacement filter. Approximate Measurements: Each filter measures 12 x 11.5 x .75 inches. Filter-Monster branded replacement replacement filter compatible with Blueair 411 Series Particle and Carbon Filter. This filter is engineered to be compatible with Blueair Pure 411, 411+, 411 Auto, and 411 Mini. To maintain peak performance, and fresh air in your home it is recommended to replace every six (6) months or more often depending on air quality and environmental factors.