FilterBySize Furnace and AC filter sizes, actual dimensions, MERV

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18x20x1 air filter: actual size, MERV, and price

An 18x20x1 is a one-inch-class rectangle furnace or AC filter. Buy the printed size 18x20x1. The panel is smaller than 18 by 20 inches — commonly 17.75 × 19.75 × 0.75, with Filtrete closer to 17.81 × 19.81 × 0.81 or 17.68 × 19.68 × 0.81 and Nordic Pure about 17.5 × 19.5 × 0.75.

Same panel, swapped axes: 20x18x1. We treat 18x20x1 as the canonical label. Order 18x20x1. Do not substitute 16x20x1 or 20x20x1 — those are different printed sizes.

Actual size by brand

These numbers are copied from manufacturer or merchant product copy, not from a competitor size chart. Thickness is part of the fit: 1-inch racks take ~¾ inch media.

Brand Nominal Published actual (in.) Source
Honeywell 1-inch Standard/High/Ultra Efficiency (MERV 8, 11, and 13) 18x20x1 17.75 × 19.75 × 0.75 Honeywell Store product specs
Filtrete 18x20x1 MPR 1000 / MERV 11 18x20x1 17.81 × 19.81 × 0.81 Amazon B0FST3KJB3 title “Actual Size 17.81 × 19.81 × 0.81 in” and product-dimensions field
Filtrete 18x20x1 MPR 1000 / MERV 11 (some listings) 18x20x1 17.68 × 19.68 × 0.81 Amazon 4-pack titles “Actual Size 17.68 × 19.68 × 0.81 in” — different figure than the 2-pack SKU; measure if the slot is tight
Filtrete 18x20x1 MPR 1900 / MERV 13 18x20x1 17.81 × 19.81 × 0.78 Amazon B0F9LTKG2W title “Act Size 17.81x19.81x0.78 in”; same-SKU product-dimensions field lists 19.81 × 17.81 × 0.81
Filtrete 18x20x1 MPR 700 / MERV 8 18x20x1 17.81 × 19.81 × 0.81 Amazon B0DKZ428BF title “Actual Size 17.81 × 19.81 × 0.81 in”
Nordic Pure 18x20x1 pleated 18x20x1 Approximately 17.5 × 19.5 × 0.75 (17½ × 19½ × ¾) JB Tools listing for Nordic Pure 18x20x1M8-24 and 18x20x1M13-24

We did not find an Amazon Basics 18x20x1 listing that publishes an actual-size field, so that brand is omitted rather than guessed. If you currently run Nordic Pure (~17.5 × 19.5) and switch to Honeywell (17.75 × 19.75) or Filtrete (~17.81 × 19.81), expect a snugger slide-in. Filtrete’s published actuals also disagree with each other by SKU. Measure the old filter if the slot is tight. Full method: how to measure.

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 1-inch MERV 13 is not HEPA. We do not claim health outcomes.

MERV EPA average capture efficiency (particle size) Typical 18x20x1 use
8 ≥20% of 1.0–3.0 µm; ≥70% of 3.0–10.0 µm Common pleated replacement when the manual does not call for higher
11 ≥20% of 0.30–1.0 µm; ≥65% of 1.0–3.0 µm; ≥85% of 3.0–10.0 µm Mid-grade 1-inch pleat (Filtrete MPR 1000 is commonly labeled 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 1-inch; confirm the furnace/air handler can take the extra pressure drop

Source: U.S. EPA, “What is a MERV rating?”, last updated 14 Jan 2026. Filtrete also prints an MPR number; MPR is 3M’s scale, not MERV. Compare MERV to MERV.

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.

Listing MERV Pack Price that day Per filter Merchant
Nordic Pure 18x20x1 pleated (reseller) 8 24 $171.89 $7.16 JB Tools
Honeywell 18x20x1 Standard Efficiency 8 12 $147.95 $12.33 Honeywell Store
Honeywell 18x20x1 Standard Efficiency 8 4 $53.95 $13.49 Honeywell Store
Honeywell 18x20x1 High Efficiency 11 12 $175.95 $14.66 Honeywell Store
Honeywell 18x20x1 High Efficiency 11 4 $63.95 $15.99 Honeywell Store
Nordic Pure 18x20x1 pleated (reseller) 13 24 $242.99 $10.12 JB Tools
Honeywell 18x20x1 Ultra Efficiency 13 12 $197.95 $16.50 Honeywell Store
Honeywell 18x20x1 Ultra Efficiency 13 4 $71.95 $17.99 Honeywell Store

Observed range that day for ordinary pleated 18x20x1: about $7.16–$13.49/filter at MERV 8 in multi-packs, $14.66–$15.99 at MERV 11, $10.12–$17.99 at MERV 13, with 4-packs costing more per filter than 12- or 24-packs. Target’s Filtrete 18x20x1 MPR 1000 1-pack page (A-14966281) loaded without a public cart price in the fetch (price API returned 403), so that pack is omitted rather than guessed. No Filtrete 18x20x1 2-pack was listed at Target. Walmart Filtrete product pages returned a bot check, so those pack prices are omitted rather than guessed. Amazon Filtrete pages were used for actual-size fields, not for this price table. Amazon Basics had no published 18x20x1 actual-size listing. A Nordic Pure 18x20x1 MERV 8 12-pack page timed out, so that pack is omitted rather than guessed; the JB Tools 24-pack is the reseller snapshot.

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 an 18x20x1 SKU. A 16x20x1 or 20x20x1 is not a substitute.

Sources (accessed 30 Aug 2026)