FilterBySize Furnace and AC filter sizes, actual dimensions, MERV

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Size page

This is a first-pass size page: actual size and MERV, not the full pack-price table yet. The complete 16x25x1 page is the model. 20x20x1 is the next money page to expand.

20x20x1 air filter: actual size and MERV

A 20x20x1 is a one-inch-class square filter. Order 20x20x1. The cut is smaller than 20 inches on each side.

Actual size by brand

BrandPublished actual (in.)Source
Honeywell 1-inch High Efficiency MERV 1119.75 × 19.75 × 0.75Honeywell Store 4-pack and 12-pack specs
Amazon Basics 20x20x1 MERV 11 6-pack19.75 × 19.75 × 0.75Amazon product title / actual size field
Filtrete 20x20x1 (one MERV 13 / MPR 1900 listing)Title: 19.62 × 19.62 × 0.78; dimensions field also shows 19.69 × 19.69 × 0.78Amazon B005GZ8IG2 — two figures on the same listing; measure if the slot is tight

We do not yet have a Nordic Pure 20x20x1 actual-size line from a product label in this pass. Do not assume it matches Honeywell’s 19.75 cut.

MERV 8 / 11 / 13

MERV does not change the nominal size. EPA’s table (ASHRAE 52.2):

MERVEPA average capture efficiency
8≥20% of 1.0–3.0 µm; ≥70% of 3.0–10.0 µm
11≥20% of 0.30–1.0 µm; ≥65% of 1.0–3.0 µm; ≥85% of 3.0–10.0 µm
13≥50% of 0.30–1.0 µm; ≥85% of 1.0–3.0 µm; ≥90% of 3.0–10.0 µm

EPA: if you upgrade, use at least MERV 13 or as high as the system fan and slot can take. Check the HVAC manual before MERV 13 in a 1-inch slot. MERV 13 is not HEPA. No health claims.

How to measure   See the 16x25x1 page for a full buy table

Sources (accessed 30 Aug 2026). EPA: What is a MERV rating?. Brand actual sizes: Honeywell Store product specs and Amazon product titles/“actual size” fields cited on this page.