Factory original replacement filter size 20" x 25" x 4" (actual width is 4.5 inches) for Honeywell media air cleaner model F200E 1037. Comes in 2-pack for reduced product and shipping costs. Manufacturer recommends replacing every 8-12 months. Can be used in the 20" x 25" x 4" Honeywell F100 or Honeywell F200 filter frame.