HVAC Label Guide

20x20x1 Air Filter: Actual Size by Maker

Last updated: 2026-10-30

A 20x20x1 air filter measures 19.5 x 19.5 x 0.75 in on a filter maker's product page, and another maker's 2026 bulletin prints it as 19-1/2 x 19-1/2 x 7/8 in. A different maker's 20x20x1 filters run 19.62 to 19.69 in on each side. Each maker cuts the filter a little under the 20 x 20 x 1 name.

“20x20x1” is the nominal size, the rounded name you order by. The actual size is what the filter measures, and it is what has to fit your slot.

The Size Each Maker Prints

Actual Size by Maker
MakerProductActual size (in)Source
FilterbuyModel AFB20x20x1M8 (pleated)19.5x19.5x0.75Filterbuy product page
GlasflossZ-Line ZL (pleated), 1 in19-1/2 x 19-1/2 x 7/8 (19.5 x 19.5 x 0.875*)Glasfloss ZL bulletin (PDF)
3M FiltreteMPR 300 (MERV 5)19.69 x 19.69 x 0.81†3M product page
3M FiltreteMPR 700 (MERV 8)19.69 x 19.69 x 0.81†3M product page
3M FiltreteMPR 1500 (MERV 12)19.62 x 19.62 x 0.78†3M product page
3M FiltreteMPR 1900 (MERV 13)19.62 x 19.62 x 0.78†3M product page

*Our conversion of the fraction Glasfloss prints. †Our match of the two size lists on each 3M product page; the other rows are as each maker prints them. MERV (Minimum Efficiency Reporting Value) is the industry filter rating; MPR is Filtrete's own rating scale.

Every maker in the table cuts the face 0.31 to 0.5 in under 20 in. Depth runs from 0.75 to 0.875 in for a filter named 1 in.

Filterbuy calls the 16x25x1 the second most ordered filter size overall after the 20x20x1.

Source: Filterbuy, 16x25x1 Air Filters page.

Deeper Filters with the Same 20 x 20 Face

A 20 x 20 slot may take a thicker filter. Check the depth printed on your old filter before you order.

Deeper Filters with the Same Face
MakerProductSize as the maker prints it (in)Source
GlasflossZ-Line ZL, 4 in20 x 20 x 4 nominal; 19-1/2 x 19-1/2 x 3-3/4 actual (19.5 x 19.5 x 3.75*)Glasfloss ZL bulletin (PDF)
Honeywell Home (Resideo)FC200E101120 X 20 X 4Resideo filter guide (PDF)
Honeywell Home (Resideo)FC100A1011 and POPUP202020 X 20 X 5Resideo filter guide (PDF)

Decimal inches in parentheses, marked *, are our conversion of the fractions Glasfloss prints. Resideo's guide gives no actual size for these filters. More on Honeywell sizes: Honeywell media filters.

How to Pick the Right 20x20x1

  1. Read the size printed on the frame of the filter you have now.
  2. If it says 20x20x1, any row in the first table is cut to fit that slot.
  3. If it is thicker than 1 in, use the second table or your cabinet maker's part number.

Which way the airflow arrow on the frame points and how to measure a filter with no size printed: Find your filter size.

Other sizes: 16x25x1, 20x25x1, 16x20x1 and 16x25x4. See also: Nominal vs. Actual Size. All Filter Sizes.

Sources

  1. Filterbuy, 20x20x1 air filters product page (“Actual Size”, model AFB20x20x1M8): https://filterbuy.com/air-filters/20x20x1/
  2. Filterbuy, 16x25x1 Air Filters page (updated August 14, 2026): https://filterbuy.com/air-filters/16x25x1/
  3. Glasfloss, Z-Line ZL series product bulletin 6ZLINEZL, dated 3/10/26 (PDF), “ZL Standard Size Filters” table: https://www.glasfloss.com/wp-content/uploads/2025/10/06baBro0326ZL.pdf
  4. 3M, Filtrete MPR 300 Basic Dust & Lint Air Filters (1”) product page (undated): https://www.filtrete.com/3M/en_US/p/d/b10262193/
  5. 3M, Filtrete MPR 700 Dust, Pollen & Pet Dander Reduction Air Filters (1”) product page (undated): https://www.filtrete.com/3M/en_US/p/d/b10014744/
  6. 3M, Filtrete MPR 1500 Allergen, Bacteria & Virus Air Filters (1”) product page (undated): https://www.filtrete.com/3M/en_US/p/d/b10014262/
  7. 3M, Filtrete MPR 1900 Premium Allergen, Bacteria & Virus Air Filters (1”) product page (undated): https://www.filtrete.com/3M/en_US/p/d/b00039899/
  8. Resideo, Honeywell Home Filter Replacement Guide, form 50-1312 (08/20, PDF): https://customer.resideo.com/resources/Techlit/TechLitDocuments/50-0000s/50-1312.pdf