18x24x5 (17.75x23.75x4.38) MERV 13 Aftermarket Honeywell Replacement Filter (2 Pack) Nominal size 18" x 24" x 5". Actual size 17 3/4" x 23 3/4" x 4 3/8". 98% efficient filtration media capturing particles as small as 0.3 microns before they can collect on your coils. High-efficiency alternative to one-inch filters. Larger media capacity allows for greater dust-holding ability. This is an aftermarket filter.