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20x20x3 air filter: actual size, MERV, and price

A 20x20x3 is a three-inch-class square filter. On this size that usually means a return-grille cartridge — a 3-inch-deep pack that seats in a 1-inch grille with the extra depth hanging into the duct — not a 20x20x2 furnace-slot pack. Buy the printed size 20x20x3. Do not substitute a 20x20x1. A 20x20x2 is about 1.75 inches thick. A 20x20x4 / 20x20x5 is four-inch cabinet media, about 3.63–4.38 inches thick. Those are not drop-in swaps for this 3-inch class.

Honeywell Store lists FC40R1003 as a 20×20 return-grille filter (MERV 10). Honeywell Home lists a MERV 13 20×20 return-grille filter (FC313R2020) with published product size 19.75 × 19.75 × 3.13. Filtrete, Nordic Pure / JB Tools, and Amazon Basics do not list a 20x20x3 SKU with a printed actual this check. No ordinary 19.5 × 2.75 furnace-slot 20x20x3 pack turned up with a published actual, so that 2.75-inch figure is omitted rather than guessed.

Actual size by brand

These numbers are copied from manufacturer or merchant product copy, not from a competitor size chart. Thickness is the fit problem on this size: a 3-inch return-grille cartridge is not a 1.75-inch 20x20x2, and it is not 4-inch cabinet media. Face size is not one number either — Honeywell prints about 19.75 square; Zephyr and AIRx print about 18.375 square behind a gasket that fills a 20-inch grille.

Brand Nominal Published actual (in.) Source
Honeywell FC40R1003 return-grille media (MERV 10) 20x20x3 Current merchant copy: 19-3/4 × 19-3/4 × 3. OEM spec sheet 68-3062-06 Table 1 still prints face 19-3/4 × 19-3/4, media 18-1/2 × 18-1/2, depth 4-3/8 DiscountFilters listing “actual size 19 3/4 × 19 3/4 × 3” and note that Honeywell now makes this in 3-inch depth (formerly 4-3/8). Honeywell spec 68-3062-06 (Air Quality Honeywell Store PDF) is the older 4-3/8 figure. Not a 19.5 × 1.75 furnace-slot pack
Honeywell Home FC313R2020 return-grille media (MERV 13) 20x20x3 19.75 × 19.75 × 3.13 Honeywell Home “MERV 13 Return Grille Filters” specs for 20 × 20: product length 19.75 in, height 19.75 in, width 3.13 in. Resideo 50-8985 lists FC313R2020 as 20″ × 20″ × 3″ MERV 13. No public cart price this check
Zephyr VGF 20x20x3 (M1132020 MERV 11 / M1332020 MERV 13) 20x20x3 18.375 × 18.375 × 3 Jackson Systems M1332020 “Actual size: 18.375″ × 18.375″ × 3″ (nominal size: 20x20x3)”. J Adams M1332020 “Actual Dimensions: 18.375 × 18.375 × 3”. Top-hat gasket seats in a 1-inch grille
AIRx 202003RG return-grille (MERV 8 / 11 / 13) 20x20x3 Outside including gasket: 20 × 20 × 3; inside: 18 3/8 × 18 3/8 × 3 DiscountFilters listings for 202003RG-DUST, 202003RG-ALLERGY, and 202003RG-HEALTH. Copy: gasket fits a 1-inch slot with the extra depth in the duct. Labeled as replacing Honeywell FC40R1003 / FC20R2020

If you currently run a Honeywell FC40R / FC313R (~19.75 square) and switch to Zephyr or AIRx (~18.375 square plus gasket), you are changing product class, not just brand. A 20x20x2 (~19.5 × 1.75) will not fill a 3-inch return-grille depth. A 20x20x4 Nordic Pure (~19.5 × 3.63) or Honeywell FC100/FC200 (~4.38) is cabinet media, not this size. Measure the old filter if the grille is tight. Full method: how to measure.

Filtrete: no 20x20x3 SKU with a printed actual this check (3M’s 20×20 line in this check is 1-inch, 2-inch, and 4-inch). Nordic Pure / JB Tools: no 20x20x3 SKU this check (20x20x2 prints ~19.5 × 1.75; 20x20x4 prints ~19.5 × 3.63). Amazon Basics: no 20x20x3 SKU with a printed actual this check. Filterbuy’s Honeywell FC40R replacement is sold as 20x20x5 with printed actual 18.38 × 18.38 × 3.69 — that is a different nominal, so it is omitted here. No merchant in this check printed a 2.75-inch 20x20x3 furnace-slot actual.

MERV 8 vs 11 vs 13 (facts only)

MERV is ASHRAE 52.2, as summarized by EPA. Higher MERV captures a larger share of smaller particles. It also adds resistance. EPA says to pick at least MERV 13 or as high a rating as your system fan and filter slot can accommodate, and to ask an HVAC technician if you are unsure. A 3-inch MERV 13 is not HEPA. We do not claim health outcomes.

MERV EPA average capture efficiency (particle size) Typical 20x20x3 use
8 ≥20% of 1.0–3.0 µm; ≥70% of 3.0–10.0 µm Common return-grille 3-inch replacement when the manual does not call for higher (AIRx 202003RG-DUST)
11 ≥20% of 0.30–1.0 µm; ≥65% of 1.0–3.0 µm; ≥85% of 3.0–10.0 µm Mid-grade 3-inch return-grille pleat (Zephyr VGF M1132020; AIRx 202003RG-ALLERGY). Honeywell FC40R1003 in this check is MERV 10, not MERV 11
13 ≥50% of 0.30–1.0 µm; ≥85% of 1.0–3.0 µm; ≥90% of 3.0–10.0 µm Higher-efficiency 3-inch return-grille (Zephyr VGF M1332020; AIRx 202003RG-HEALTH; Honeywell FC313R2020). Confirm the system can take the extra pressure drop. Not HEPA

Source: U.S. EPA, “What is a MERV rating?”, last updated 14 Jan 2026. Honeywell FC40R1003 is labeled MERV 10 (price row below); EPA’s table still uses the 8 / 11 / 13 steps shown here.

Pack prices checked 30 Aug 2026

These are public shelf/cart prices we recorded on 30 Aug 2026. They are not live. Shipping, subscribe-and-save, and store-only deals will move them. Per-filter math is pack price ÷ count, rounded to the cent. Honeywell Store’s 20x20x3 row is the FC40R1003 return-grille SKU, not a 19.5 × 1.75 furnace-slot pack. Nordic Pure has no 20x20x3 row.

Listing MERV Pack Price that day Per filter Merchant
Zephyr 20x20x3 VGF return-grille 11 3 $97.95 $32.65 Filters Delivered
AIRx 20x20x3 return-grille 8 4 $156.99 $39.25 DiscountFilters
Zephyr 20x20x3 VGF return-grille 13 3 $119.95 $39.98 Filters Delivered
Zephyr 20x20x3 VGF return-grille 13 2 $82.95 $41.48 Filters Delivered
AIRx 20x20x3 return-grille 8 2 $84.95 $42.48 DiscountFilters
AIRx 20x20x3 return-grille 11 2 $89.95 $44.98 DiscountFilters
AIRx 20x20x3 return-grille 13 2 $98.99 $49.50 DiscountFilters
Honeywell FC40R1003 return-grille 10 2 $171.99 $86.00 DiscountFilters
Honeywell FC40R1003 return-grille 10 1 $94.50 $94.50 Honeywell Store

Observed range that day for 20x20x3 return-grille packs: about $33/filter at MERV 11 in a Zephyr 3-pack, $39–$45 at MERV 8 / 11 on AIRx packs, $40–$50 at MERV 13, with Honeywell OEM FC40R1003 (MERV 10) at about $86–$95. Target Filtrete has no 20x20x3 listing this check. Target Zephyr A-1009287596 (box of 2) loaded without a public cart price, so that pack price is omitted rather than guessed. Amazon 20x20x3 listings were bot-blocked or out of stock this check; no Amazon cart price recorded. Honeywell Home FC313R2020 has no public cart price this check. Home Depot has no 20x20x3 HVAC SKU this check. Amazon Basics has no 20x20x3 SKU in this check. Filtrete and Nordic Pure / JB Tools have no 20x20x3 furnace or return-grille SKU in this check.

Where to buy

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No ranking. Stock and price change. If the slot is an odd fraction that none of these actual sizes match, measure first — that is not a 20x20x3 SKU. A 20x20x1 is not a substitute. A 20x20x2 is a ~1.75-inch furnace-slot pack, not this 3-inch return-grille class. A 20x20x4 is four-inch cabinet media (~3.63–4.38), not this size. Honeywell FC40R1003 / FC313R2020 are return-grille cartridges, not 19.5 × 1.75 furnace filters.

Sources (accessed 30 Aug 2026)