HVAC Label Guide

20x25x1 air filter: actual size by maker

“20x25x1” is the nominal size, the rounded name printed on the frame. The filter itself is a little smaller, and the exact cut depends on the maker.

20 x 25 x 1 in nominal
Filterbuy: 19.5x24.5x0.75 in actual. Glasfloss ZL: 19-1/2 x 24-1/2 x 7/8 in exact.
Sources: Filterbuy 20x25x1 product page (accessed 2026-10-27); Glasfloss Z-Line ZL product bulletin 6ZLINEZL (PDF, dated 3/10/26), “ZL Standard Size Filters” table (accessed 2026-10-27). Last checked 2026-10-27.

Actual size by maker

MakerProductNominalActual size as the maker prints it (in)Source
FilterbuyModel AFB20x25x1M8 (pleated, 1 in)20x25x119.5x24.5x0.75Filterbuy product page (accessed 2026-10-27)
GlasflossZ-Line ZL series (pleated)20 x 25 x 119-1/2 x 24-1/2 x 7/8ZL product bulletin (PDF) (accessed 2026-10-27)

Filterbuy prints decimals and Glasfloss prints fractions. We copy both as printed. Glasfloss rates the ZL at MERV 10. We list it because Glasfloss publishes its exact cut sizes.

The two makers cut the same length and width. Only the depth differs. If your slot is tight front to back, compare the depth figure before you switch brands.

Same face size, deeper filters

Some returns and filter cabinets take a 2 in or 4 in filter with the same face size. Glasfloss lists these exact sizes for its ZL series:

Nominal (in)Exact, Glasfloss ZL (in)
20 x 25 x 219-1/2 x 24-1/2 x 1-3/4

Source: Glasfloss Z-Line ZL product bulletin 6ZLINEZL (PDF, dated 3/10/26), “ZL Standard Size Filters” table (accessed 2026-10-27). A media cabinet made for one maker's filter may need that maker's part. See our AprilAire pages for two examples.

How to use these numbers

  1. Read the nominal size printed on the frame of the filter you have now.
  2. Measure the old filter's length, width and depth with a tape measure.
  3. Compare your measurements with the actual sizes above. Pick the maker whose cut matches your old filter most closely.

Nordic Pure gives the same advice: “the actual size is the precise measurement of the filter, which is usually slightly smaller.” Read more on our nominal vs actual size page. Other sizes: 16x25x1 and 16x20x1.

Not yet on this page

We list a maker only after we read the actual size on that maker's own page. Nordic Pure's product page did not show its actual size when we read it, and 3M's Filtrete page did not list one. We left both out rather than copy figures from retailers or competitors.

No affiliate links are live on this site. If we add any, we will mark them and explain them on our disclosure page. Links never change a size or a date rule.

Sources

  1. Filterbuy, 20x25x1 air filters product page (“Actual Size”, model AFB20x25x1M8): https://filterbuy.com/air-filters/20x25x1/, accessed 2026-10-27
  2. Glasfloss, Z-Line ZL series product bulletin 6ZLINEZL, dated 3/10/26 (PDF): https://www.glasfloss.com/wp-content/uploads/2025/10/06baBro0326ZL.pdf, linked from https://www.glasfloss.com/product/zl/, accessed 2026-10-27
  3. Nordic Pure, What is nominal size vs actual size?: https://www.nordicpure.com/what-is-nominal-size-vs-actual-size/, accessed 2026-10-27

Last checked 2026-10-27.