FilterBySize Furnace and AC filter sizes, actual dimensions, MERV

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18x18x1 air filter: actual size, MERV, and price

A 18x18x1 is a one-inch-class square furnace or AC filter. Buy the printed size 18x18x1. The panel is smaller than 18 inches on each face — Filtrete closer to 17.68 × 17.68 × 0.81 or 17.81 × 17.81 × 0.81, and Nordic Pure about 17.75 × 17.75 × 0.75. Do not substitute 18x20x1 or 18x24x1 — 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
Filtrete 18x18x1 MPR 1000 / MERV 11 18x18x1 Title: 17.68 × 17.68 × 0.81; dimensions field also 17.81 × 17.81 × 0.81 Amazon B07FP5X4GW — two figures on the same listing; B005GZ8PEC 4-pack title and dimensions field print the same pair; measure if the slot is tight
Filtrete 18x18x1 MPR 1000 / MERV 11 2-pack 18x18x1 17.81 × 17.81 × 0.81 Amazon B0FST2RGV8 title “Actual Size 17.81 × 17.81 × 0.81 in”; product-dimensions field lists 17.81 × 17.81 × 0.81
Filtrete 18x18x1 MPR 700 / MERV 8 18x18x1 17.81 × 17.81 × 0.81 Amazon B0DLPTXMN2 title “Actual Size 17.81 × 17.81 × 0.81 in”; product-dimensions field lists 17.81 × 17.81 × 0.81
Filtrete 18x18x1 MPR 1900 / MERV 13 18x18x1 17.81 × 17.81 × 0.78 Amazon B07FNQWZSC title “Act Size 17.81×17.81×0.78 in”; product-dimensions field lists 17.81 × 0.78 × 17.81
Nordic Pure 18x18x1 pleated 18x18x1 Approximately 17.75 × 17.75 × 0.75 (17¾ × 17¾ × ¾) JB Tools listings for Nordic Pure 18x18x1M8-6, 18x18x1M8-2, 18x18x1M13-6, and 18x18x1M13-2

We did not find a Honeywell Store 18x18x1 1-inch SKU (MERV 8/11/13 4-pack or 12-pack) that publishes actual dimensions, so that brand is omitted rather than guessed. Nearby listed Honeywell 1-inch sizes include 18x20x1. We did not find an Amazon Basics 18x18x1 listing that publishes an actual-size field, so that brand is omitted rather than guessed. If you currently run Nordic Pure (~17.75 square) and switch to Filtrete (~17.68 or 17.81 square), expect a slightly different 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 18x18x1 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 18x18x1 pleated (reseller) 8 2 $29.24 $14.62 JB Tools
Nordic Pure 18x18x1 pleated (reseller) 8 6 $50.39 $8.40 JB Tools
Nordic Pure 18x18x1 pleated (reseller) 13 2 $31.49 $15.75 JB Tools
Nordic Pure 18x18x1 pleated (reseller) 13 6 $62.99 $10.50 JB Tools

Observed range that day for ordinary pleated 18x18x1: about $8.40/filter at MERV 8 in a Nordic Pure 6-pack, $10.50 at MERV 13 in a Nordic Pure 6-pack, with 2-packs costing more per filter ($14.62 MERV 8; $15.75 MERV 13). Honeywell Store product URLs for 18x18x1 MERV 8/11/13 4-packs and 12-packs returned 404, so those rows are omitted rather than guessed. Target listed a Filtrete 18x18x1 MPR 1000 1-pack (A-14436498); that product page loaded without a public cart price and Target’s price API returned a bot check (403), so that pack price is omitted rather than guessed. Walmart Filtrete product pages were not used for this check (Target Filtrete preferred). Amazon Filtrete pages were used for actual-size fields, not for this price table. Amazon Basics had no published 18x18x1 actual-size listing. Nordic Pure’s own 18x18x1 factory cart was not used for a 1-inch SKU in this check; the JB Tools figures are reseller snapshots. A 18x18x1 is not a 18x20x1 or a 18x24x1.

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 18x18x1 SKU. A 18x20x1 or 18x24x1 is not a substitute.

Sources (accessed 30 Aug 2026)