FilterBySize Furnace and AC filter sizes, actual dimensions, MERV

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18x24x1 air filter: actual size, MERV, and price

An 18x24x1 is a one-inch-class furnace or AC filter. Buy the printed size 18x24x1. The panel is smaller than 18 by 24 inches — Filtrete closer to 17.81 × 23.81 × 0.81 or 17.68 × 23.68 × 0.81 and Nordic Pure about 17.5 × 23.5 × 0.75.

Same panel, swapped axes: 24x18x1. We treat 18x24x1 as the canonical label. Order 18x24x1. Do not substitute 16x24x1, 18x20x1, or 20x24x1 — 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 18x24x1 MPR 1000 / MERV 11 18x24x1 17.81 × 23.81 × 0.81 Amazon B07CTPTG7Z product-dimensions field lists 23.81 × 17.81 × 0.81; B07FNW3PV6 product-dimensions field lists 23.78 × 17.81 × 0.81; B005GZ8WIG product-dimensions field lists 23.81 × 0.81 × 17.81
Filtrete 18x24x1 MPR 1000 / MERV 11 (some listings) 18x24x1 17.68 × 23.68 × 0.81 Amazon B07CTPTG7Z, B07FNW3PV6, and B005GZ8WIG titles “Actual Size 17.68 × 23.68 × 0.81 in”
Filtrete 18x24x1 MPR 300 / MERV 5 18x24x1 17.81 × 23.81 × 0.81 Amazon B07FNW9WZ1 title “Actual Size 17.81x23.81x0.81 in”
Filtrete 18x24x1 MERV 5 6-pack (some listings) 18x24x1 17.81 × 23.81 × 0.88 Amazon B0D96SVNZS title “Actual Size 17.81x23.81x0.88 in”; product-dimensions field lists 23.81 × 0.88 × 17.81
Filtrete 18x24x1 MPR 1500 / MERV 12 18x24x1 17.81 × 23.81 × 0.78 Amazon B00TUDHVIW title “Act. Size 17.81x23.81x0.78 in”; same-SKU product-dimensions field lists 19.81 × 0.78 × 17.81
Nordic Pure 18x24x1 pleated 18x24x1 Approximately 17.5 × 23.5 × 0.75 (17½ × 23½ × ¾) JB Tools listing for Nordic Pure 18x24x1M8-12 and 18x24x1M13-12

We did not find a Honeywell Store 18x24x1 1-inch SKU (MERV 8/11/13 4-pack or 12-pack) that publishes actual dimensions, so that brand is omitted rather than guessed. We did not find an Amazon Basics 18x24x1 listing that publishes an actual-size field, so that brand is omitted rather than guessed. If you currently run Nordic Pure (~17.5 × 23.5) and switch to Filtrete (~17.81 × 23.81), 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 18x24x1 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 18x24x1 pleated (reseller) 8 12 $87.29 $7.27 JB Tools
Nordic Pure 18x24x1 pleated (reseller) 13 12 $121.49 $10.12 JB Tools

Observed range that day for ordinary pleated 18x24x1: about $7.27/filter at MERV 8 in a Nordic Pure 12-pack, $10.12 at MERV 13 in a Nordic Pure 12-pack. Honeywell Store product URLs for 18x24x1 MERV 8/11/13 4-packs and 12-packs returned 404, so those rows are omitted rather than guessed. Target listed a Filtrete 18x24x1 MPR 1000 1-pack (A-15113308) and 2-pack (A-51925606); those product pages and Target’s price API returned a bot check or no public cart price, 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 18x24x1 actual-size listing.

Where to buy

We may earn a commission if you buy through links on this page. It does not change the price you pay.

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 18x24x1 SKU. A 16x24x1, 18x20x1, or 20x24x1 is not a substitute.

Sources (accessed 30 Aug 2026)