Air filter sizes: nominal and actual, by maker
Last updated: 2026-10-27
Filterbuy and Glasfloss cut 16x25x1, 20x25x1 and 16x20x1 filters about half an inch under nominal in length and width. AprilAire's 213 and 413 media filters are wider than their nominal 25 in.
| Nominal | Filterbuy actual (in) | Glasfloss ZL exact (in) |
|---|
| 16x25x1 | 15.5x24.5x0.75 | 15-1/2 x 24-1/2 x 7/8 |
| 20x25x1 | 19.5x24.5x0.75 | 19-1/2 x 24-1/2 x 7/8 |
| 16x20x1 | 15.5x19.5x0.75 | 15-1/2 x 19-1/2 x 7/8 |
| Cabinet | Filter | Nominal (AprilAire) | Actual (AprilAire) |
|---|
| AprilAire 2210 | 213 | 20H x 25W x 4D | 20.6H x 26.63W x 4D |
| AprilAire 2410 | 413 | 16H x 25W x 4D | 16.52H x 29.38W x 4D (unconfirmed by a second AprilAire document) |
Sources: Filterbuy product pages for 16x25x1, 20x25x1 and 16x20x1; Glasfloss Z-Line ZL product bulletin 6ZLINEZL (PDF, dated 3/10/26), “ZL Standard Size Filters” table (accessed 2026-10-27); AprilAire 213 filter page (accessed 2026-10-27); AprilAire 413 filter page (accessed 2026-10-27).
Pages by size and cabinet
Why the two sizes differ: nominal vs actual size. Serial numbers: All date codes.