HVAC Label Guide

20x25x1 air filter: actual size by maker

Last updated: 2026-10-27

“20x25x1” is the nominal size, the rounded name printed on the frame. Its actual size by maker: Filterbuy 19.5x24.5x0.75 in, Glasfloss ZL 19-1/2 x 24-1/2 x 7/8 in.

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).

What size does each maker cut?

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. Glasfloss rates the ZL at MERV 10.

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.

Is there a deeper filter with the same face size?

Some returns and filter cabinets take a 2 in filter with the same face size. Glasfloss lists this exact size 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 do I 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. All filter sizes.

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