HVAC Label Guide

20x25x4 Air Filter: Actual Size by Maker

Last updated: 2026-10-30

A pleated (folded) 20x25x4 air filter measures 19.5 x 24.5 x 3.63 in on two filter makers' product pages. Some filters made for whole-house media cabinets, the filter boxes next to a furnace, have the same 20 x 25 face (height and width) but run deeper, 4.31 to 4.38 in. One cabinet maker's 2025 bulletin lists that deeper filter as 20 x 25 x 5.

“20x25x4” is the nominal size, the rounded name you order by. The actual size is what the filter measures. The face size is the height and width, without the depth. A pleated filter has its filter material folded like an accordion. A media cabinet is a whole-house filter box next to the furnace that holds a thick filter. Read across for the actual size each maker prints.

The Size Each Maker Prints

Actual Size by Maker
MakerProductSize name the maker usesActual size as the maker prints it (in)Source
FilterbuyModel AFB20x25x4M8 (pleated)20x25x419.5x24.5x3.63Filterbuy product page
Nordic PurePleated, 4 in20x25x419 1/2 x 24 1/2 x 3 5/8 (19.5 x 24.5 x 3.63)Nordic Pure product page
3M FiltreteMPR 1550 (MERV 12), 4 in20 in X 25 in19.75 x 24.63 x 4.31 or 19.88 x 24.63 x 4.31 (both listed)*3M product page
LennoxFilters X6673, 19L17 and X6675 for the Healthy Climate HCC20-28 cabinet20 x 25 x 519-3/4 x 24-3/4 x 4-3/8 (19.75 x 24.75 x 4.38*)Lennox HCC bulletin (PDF)
CarrierFILXXCAR0020, for the 20 in FILCAB cabinet20 in cabinet24.75 x 19.875 x 4.3125 (Carrier lists length first)Carrier FILCAB data sheet (PDF)
AprilAire213, for the 2210 air purifier (AprilAire's name for its media cabinet)20H x 25W x 4D20.6H x 26.63W x 4DAprilAire 213 filter page
Honeywell Home (Resideo)FC100A103720 X 25 X 4 and 20 X 25 X 5, both printedNot printed in the guideResideo filter guide (PDF)

*Decimals for Lennox are our conversion of its fractions. The 3M row is our match of the two size lists on its product page. The other rows are as each maker prints them. H, W and D mean height, width and depth. MERV (Minimum Efficiency Reporting Value) is the industry filter rating; MPR is Filtrete's own rating scale.

The pleated filters from two makers match to the hundredth of an inch. The 3M, Lennox and Carrier filters for media cabinets are deeper, 4.31 to 4.38 in. AprilAire's 213 is 4 in deep but 26.63 in wide for a 25 in nominal width. See AprilAire 2210 and the 213 filter.

Why Two Depths Share One Name

Resideo's guide prints the same Honeywell filter, FC100A1037, as both 20 X 25 X 4 and 20 X 25 X 5. Lennox calls its 4-3/8 in deep filter a 20 x 25 x 5. So the face size alone does not tell a 3.63 in pleated filter from a 4.31 to 4.38 in media filter. Measure the depth of your old filter before you order.

Sources: Resideo, Honeywell Home Filter Replacement Guide 50-1312 (PDF); Lennox, Healthy Climate media air cleaners bulletin (PDF).

How to Pick the Right 20x25x4

  1. Read the size name and any part number on the frame of the filter you have now.
  2. Measure its depth with a tape measure.
  3. If it is about 3.6 in deep, a pleated 20x25x4 from the first two rows matches. If it is about 4.3 to 4.4 in deep, find your cabinet maker's part number on the filter size by brand page.

Other ratings for the same size: Filterbuy lists its 20x25x4 at MERV 8, 11 and 13. Our Filtrete MPR to MERV chart converts 3M's MPR numbers.

Source: Filterbuy 20x25x4 product page.

Other sizes: 20x25x1 and 16x25x1. See also: Honeywell Media Filters, Nominal vs. Actual Size. All Filter Sizes.

Sources

  1. Filterbuy, 20x25x4 air filters product page (“Actual Size”, model AFB20x25x4M8): https://filterbuy.com/air-filters/20x25x4/, accessed 2026-10-30
  2. Nordic Pure, 20x25x4 Air Filter product page (“Actual Size”): https://www.nordicpure.com/product/20x25x4-air-filter/, accessed 2026-10-28
  3. 3M, Filtrete MPR 1550 Allergen, Bacteria & Virus Air Filters (4” and 5” Lennox) product page (undated): https://www.filtrete.com/3M/en_US/p/d/b5005595006/, accessed 2026-10-28
  4. Lennox, Healthy Climate HCC media air cleaners bulletin, form 210450 (August 2025, PDF): https://www.lennox.com/dA/a1d2030a9b/ehb_hcc_2508.pdf, accessed 2026-10-28
  5. Carrier, FILCAB and FILCAR media filter product data, catalog FLCB-04PD (edition 09/11, PDF): https://ia.cappusa.com/ZDMaOBgxD3qjtL_-ggBhMr_7uu34GH9wHoWMtVnD/data-sheet-carrier-filcabxl0016-filcabxl0020-filcabxl0024-filxxcar0116-filxxcar0120.pdf, accessed 2026-10-28
  6. AprilAire, 213 MERV 13 Air Filter: https://shop.aprilaire.com/products/aprilaire-213-replacement-filter, accessed 2026-10-27
  7. Resideo, Honeywell Home Filter Replacement Guide, form 50-1312 (08/20, PDF): https://customer.resideo.com/resources/Techlit/TechLitDocuments/50-0000s/50-1312.pdf, accessed 2026-10-28