Actual size is 20.1 x 21.1 x 5. Accumulair brand: 21x21.5x5 Honeywell TRN2121T1 replacement whole house filters, specifically designed to be an alternative to the original manufacturer Honeywell TRN2121T1 filters. Fully box-formed with no assembly or combs required. MERV classified to ASHRAE ratings ensuring particle capture as good or better than the OEM Honeywell TRN2121T1 air filters. Notice: The example air filter picture as displayed is not true to size and is there to show configuration purposes. Company names and Honeywell TRN2121T1 identifier used for air filter replacement identification only.