Size directory

Furnace filter sizes: find your exact replacement

The number on the cardboard frame is the size you order. It is a rounded label, not the tape-measure reading. Pick the printed size below, then check the actual dimensions on the size page before you buy.

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Size finder

No size on this list matches that. Try the printed whole-inch number, or measure the old filter.

Those “typical actual” figures are a shorthand. Brands cut the same label size differently — see each size page. More sizes will be added; all listed sizes.

How to read the number on the filter

The frame is printed with three numbers, almost always in inches, in this order:

Width — one face dimension (example: 16).
Length — the other face dimension (example: 25).
Thickness — how deep the slot is (example: 1, 2, 4, or 5).

So 16x25x1 means a one-inch-class filter whose shopping size is 16 by 25 inches. Buy that printed size. Do not order the fractional number your tape measure shows, or the replacement will be too small or will not go in.

If the print is faded, pull the filter out, measure length, width, and thickness, and round each face dimension up to the nearest whole inch. A filter that measures about 15.75 by 24.75 by 0.75 is a 16x25x1.

Width and length can swap on the label (25x16x1 is the same size as 16x25x1). We list the conventional smaller-or-standard × longer × thickness form.

Measure before you reorder

Nominal vs. actual is the usual reason a new filter does not fit. A 16x25x1 is usually about 15.75 × 24.75 × 0.75 inches, but Filtrete, Honeywell, Nordic Pure, and Amazon Basics do not cut it identically.

How to measure a furnace filter

1-inch actual-size chart by brand

MERV 8 vs 11 vs 13 (EPA facts)

MERV 8 vs 11 vs 13

After you know the printed size, pick a MERV rating your system fan and filter slot can handle. EPA capture efficiencies for MERV 8, 11, and 13 — facts only, no health-outcome claims.

MERV 8 vs 11 vs 13: which filter to buy

How often to change the filter

Thickness and household load matter more than a single calendar rule. Typical bands: thin 1-inch filters about every 1–3 months; 4–5 inch media about every 6–12 months. Summer AC still uses the same slot.

How often to change a furnace filter

Seasonal change reminder

Use spring and fall as calendar anchors to check the same heat/AC return slot — then replace when thickness, pets, or a clogged look say so.

Seasonal furnace filter change reminder

Wildfire smoke

Smoke and ash load filters faster. Change sooner than the usual thickness band when outdoor air is smoky or the media looks gray — size first, then MERV your system can handle.

Wildfire smoke: change your filter sooner

New home / move-in checklist

Replace the prior owner’s return filter before trusting it. Read printed size, measure if missing, pick MERV your system can handle, and stock a spare — no pack prices on this guide.

New home move-in furnace filter checklist

Humidifier pad sizes

Whole-house humidifier water panels are not furnace filters. Match AprilAire 10/12/35/45 or Honeywell HC22/HC26 from the unit sticker — no pack prices on this guide.

Humidifier pad sizes (AprilAire / Honeywell)

Mini-split / ductless filters

Wall cassette filters sit behind the indoor front panel — usually washable mesh, not a furnace 16x25x1. Match OEM parts by indoor unit model — no pack prices on this guide.

Mini-split filters (ductless wall cassette)

Return grille filters

Wall/ceiling return grilles take 1″ flat panels or 3″ top-hat media (e.g. Honeywell FC40R / FC313R) — not a media cabinet or mini-split mesh. Size first — no pack prices on this guide.

Return grille filters (1″ vs 3″ top-hat)

Honeywell FC40R return-grille media

FC40R1003 (20×20×3) and FC40R1011 (20×25×3) are MERV 10 top-hat grille cartridges — not FC100 cabinet media. Model hub has no pack prices.

Honeywell FC40R (FC40R1003 & FC40R1011)

Honeywell FC313R MERV 13 return-grille media

FC313R2020 (20×20×3) and FC313R2025 (20×25×3) are MERV 13 top-hat grille cartridges — sister to FC40R MERV 10, not FC100 cabinet media. Model hub has no pack prices.

Honeywell FC313R (FC313R2020 & FC313R2025)

Pets and allergies

Pet hair and dander load filters faster. Shop MERV 11 or 13 by printed size — size first, then a rating your system can handle. No allergy-cure claims.

Best furnace filter for pets and allergies

Filtrete MPR vs MERV

Filtrete prints MPR — 3M’s scale, not MERV. See the common MPR↔MERV map from 3M’s chart, then trust the MERV on that SKU’s box.

Filtrete MPR vs MERV

Odd and long-tail sizes

Printed size not 16x25, 20x20, or 20x25? Hub for 14x25x1, 18x24x1, 16x30x1, 20x22x1, squares, and other odd nominals — swapped-axis naming and typical actuals.

Odd furnace filter sizes

Honeywell FC100A1037 (F100/F200)

Common OEM 20x25x4 MERV 11 cartridge for Honeywell media cabinets — actual ~19.88×24.88×4.38, related CF100/CF200 packs, sister sizes, and verified OEM pack prices.

Honeywell FC100A1037 model page

Honeywell FC100A1029 (16×25 media)

Honeywell FC100A1003 (F100/F200)

Common OEM 16x20x4 MERV 11 cartridge for Honeywell media cabinets — actual 15⅞×19⅞×4⅜, sister sizes FC100A1029 / FC100A1037, and verified OEM pack prices.

Honeywell FC100A1003 (16×20 media)

Honeywell FC200E1029 (F100/F200 MERV 13)

MERV 13 charged-media OEM for Honeywell 16×25 F100/F200 cabinets — sister of FC100A1029 (MERV 11), actual 15⅞×24⅞×4⅜, verified OEM pack prices.

Honeywell FC200E1029 (16×25 MERV 13)

Honeywell FC100A1011 (F100/F200)

Common OEM 20x20x4 MERV 11 cartridge for Honeywell media cabinets — actual 19⅞×19⅞×4⅜ (Resideo 19.94×19.75×4.38), sister sizes FC100A1029 / FC100A1003 / FC100A1037, and verified OEM pack prices.

Honeywell FC100A1011 (20×20 media)

Honeywell FC200E1037 (F100/F200 MERV 13)

MERV 13 charged-media OEM for Honeywell 20×25 F100/F200 cabinets — sister of FC100A1037 (same face, MERV 11) and pair of FC200E1029 (16×25 MERV 13). Exact 19⅞×24⅞×4⅜; verified OEM pack prices.

Honeywell FC200E1037 (20×25 MERV 13)

Honeywell FC200E1011 (F100/F200 MERV 13)

MERV 13 charged-media OEM for Honeywell F100/F200 20×20 cabinets — sister of FC100A1011 (MERV 11, same face). Exact 19⅞×19⅞×4⅜.

Honeywell FC200E1011 (20×20 MERV 13)

Honeywell FC100A1052 (20×12.5 media)

Odd-size MERV 11 OEM for the Honeywell 20×12.5 media path (F27F1032) — exact 19⅞×12½×4⅜ (Resideo 19.94×12.44×4.38), sister of FC100A1011 / 1029 / 1003 / 1037, with verified OEM multi-pack prices.

Honeywell FC100A1052 (20×12.5 media)

Honeywell FC200E1003 (F100/F200 MERV 13)

MERV 13 charged-media OEM for Honeywell F100/F200 16×20 cabinets — sister of FC100A1003 (MERV 11, same face) and pair of FC200E1029 / FC200E1011 / FC200E1037. Exact 15⅞×19⅞×4⅜; verified OEM pack prices.

Honeywell FC200E1003 (16×20 MERV 13)

AprilAire 216 MERV 16 media

MERV 16 sister to 210 (MERV 11) and 213 (MERV 13) for AprilAire whole-house purifiers — same actual 20.6×26.63×4, not a Honeywell FC100A1037 drop-in. Verified OEM shop pack prices.

AprilAire 216 (MERV 16)

AprilAire 410 vs 413 (16x25x4)

AprilAire 410 vs 413

The 16x25 AprilAire cartridge for 1410, 1610, 2410, 2416, 3410 and 4400 air purifiers — 410 is MERV 11, 413 is MERV 13, same published actual 16.52×29.38×4. Not a Honeywell FC100A1029 or generic 16x25x4. AprilAire shop 1/2/4/8-pack prices with per-filter math.

AprilAire 410 vs 413

16x20x1 MERV 13

Honeywell Ultra, Filtrete MPR 1900/2200, and Nordic Pure MERV 13 for the common 16x20x1 (20x16x1) 1-inch size — pack prices and when not to run MERV 13 in a tight slot.

16x20x1 MERV 13 hub

18x24x1 MERV 13

Nordic Pure MERV 13 and Filtrete MPR 1900 for the common 18x24x1 (24x18x1) 1-inch size — pack prices and when not to run MERV 13 in a tight slot. No Honeywell Ultra SKU in this size.

18x24x1 MERV 13 hub

20x24x1 MERV 13

Honeywell Ultra Efficiency (4- and 12-pack) and Nordic Pure MERV 13 for the 20x24x1 (24x20x1) 1-inch size — actual 19.75 × 23.75 × 0.75, pack prices, and when not to run MERV 13 in a tight slot.

20x24x1 MERV 13 hub

14x20x1 MERV 13

Honeywell Ultra Efficiency MERV 13 (4- and 12-pack) and Nordic Pure MERV 13 12-pack for the 14x20x1 (20x14x1) 1-inch size — actual 13.75 × 19.75 × 0.75, pack prices, and when not to run MERV 13 on a small return.

14x20x1 MERV 13 hub

20x22x1 MERV 13

Nordic Pure MERV 13 4-, 6- and 12-pack for the less common 20x22x1 (22x20x1) 1-inch size — actual 19.5 × 21.44 × 0.75 vs Filtrete 19.81 × 21.81 × 0.81, pack prices, and why there is no Honeywell 20x22x1.

20x22x1 MERV 13 hub

25x25x1 MERV 13

Nordic Pure MERV 13 2-, 3-, 4- and 6-pack for the square 25x25x1 1-inch size — actual 24.5 × 24.5 × 0.75 vs Filtrete 24.81 × 24.81 × 0.81, pack prices (the 4-pack is lowest per filter), and why there is no Honeywell 25x25x1.

25x25x1 MERV 13 hub

24x24x1 MERV 13

Nordic Pure MERV 13 2-, 3-, 4- and 6-pack for the square 24x24x1 1-inch size — actual 23.38 × 23.38 × 0.75 vs Filtrete MPR 1900 23.81 × 23.81 × 0.78, pack prices (the 6-pack is lowest per filter), and why there is no Honeywell 24x24x1.

24x24x1 MERV 13 hub

12x24x1 MERV 13

Honeywell Ultra Efficiency 4- and 12-pack, Filtrete MPR 1900 2- and 6-pack on Amazon, and Nordic Pure MERV 13 2- to 24-packs for the narrow 12x24x1 (24x12x1) size — actual 11.75 × 23.75 × 0.75 (Honeywell) vs 11.68 × 23.68 × 0.78 (Filtrete), per-filter math, and why MERV 13 needs a fan check on a small slot.

12x24x1 MERV 13 hub

14x24x1 MERV 13

Nordic Pure MERV 13 2- to 24-packs, Filtrete MPR 1900 2- and 6-pack on Amazon, and Honeywell Ultra Efficiency 4- and 12-pack for the less common 14x24x1 (24x14x1) size — actual 13.75 × 23.75 × 0.75 (Honeywell, Nordic Pure) vs 13.81 × 23.81 × 0.78 (Filtrete), per-filter math, and why MERV 13 needs a fan check on a smaller slot.

14x24x1 MERV 13 hub

6-pack vs 12-pack cost

For 20x25x1, compare $/filter across Filtrete 6-packs and Honeywell 12-packs before you stock a year of filters.

6-pack vs 12-pack (20x25x1)