# Furnace Filter Sizes, Nominal vs Actual: What a 16x25x1 Really Measures, and Which 4 in Media Filter Fits an AprilAire or Honeywell Cabinet

> A 16x25x1 measures 15.5 x 24.5 x 0.75 in at Nordic Pure; a nominal 20x25 media filter has five actual sizes; the AprilAire 410 is 16.52 x 29.38 x 4 in.

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| Source | https://ownerspec.com/air/parts/furnace-filter-sizes-nominal-vs-actual/ |
| Publisher | OwnerSpec (https://ownerspec.com/) |
| Published | 2026-10-02 |
| Updated | 2026-10-02 |
| Facts verified | 2026-10-02 |
| Disclosure | Contains affiliate links. OwnerSpec may earn a commission at no cost to the reader. |

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## Short answer

A furnace filter's nominal size is the rounded label and its actual size is the measured frame, which is smaller: Nordic Pure's help center prints 19 1/2 x 24 1/2 x 3/4 in for a 20x25x1 and its measuring guide 15.5 x 24.5 x 0.75 in for a 16x25x1, so a 1 in filter is about 3/4 in thick. Every 1 in filter of one nominal size is cut for the same slot, so a 16x25x1 owner orders a 16x25x1 at the MERV rating wanted and measures nothing. The trap is the 4 in and 5 in media filter: Nordic Pure lists five actual sizes for a nominal 20x25, from 19.5 x 24.5 x 3.63 to 20.25 x 25.38 x 5.25 in, and AprilAire's 410, labelled 16x25x4, measures 16.52 x 29.38 x 4 in and fits only cabinets 1410, 1610, 2410, 2416, 3410 and 4400. For a media cabinet, order by the cabinet model, not the nominal size.

## Fact sheet

- **Answer:** Nominal size is the rounded label; actual size is the measured frame, usually smaller. Nordic Pure prints 19 1/2 x 24 1/2 x 3/4 in for a 20x25x1 and 15.5 x 24.5 x 0.75 in for a 16x25x1. A nominal 20x25 media filter has five actual sizes at Nordic Pure, from 19.5 x 24.5 x 3.63 to 20.25 x 25.38 x 5.25 in, and AprilAire's 16x25x4 model 410 measures 16.52 x 29.38 x 4 in.
- **Applies to:** 1 in slot filters 14x20x1, 14x25x1, 16x20x1, 16x25x1, 20x20x1, 20x25x1, 20x30x1; 2 to 5 in media filters 16x25x2, 16x25x4, 20x20x4, 20x25x4, 20x25x5; AprilAire cabinets 1210, 1620, 2210, 2216, 3210, 4200 (filter 210 or 213); 1410, 1610, 2410, 2416, 3410, 4400 (filter 410); Honeywell F100 and F200 20x25 cabinets and SpaceGard 2200 (FC100A1037 or FC200E1037); F25, F27, F35, F100, F150, F200 at 16x25 (FC100A1029)
- **Compatibility basis:** Nordic Pure's help center, measuring guide, buying article and the 16x25, 20x20, 20x25x4 and 20x25x5 actual-size category pages; AprilAire shop pages for the 210, 213 and 410; Resideo catalog pages for FC100A1037/U, FC200E1037/U, FC100A1029/U and POPUP1625/U
- **Assumptions:** Nordic Pure's dimensions are its own filters and it states a tolerance of up to 1/8 in; another maker's frame can differ by a similar amount at the same nominal size.; Six 1 in sizes in the table have no maker-printed actual size readable this session; the row says so instead of carrying a number.; Filtrete's size chart and product pages timed out this session, so no Filtrete actual size appears here.
- **Method:** Dimensions, model fit lists and intervals read from Nordic Pure, AprilAire and Resideo pages on 2026-10-02; every ASIN on the page checked IN_STOCK through the Amazon Creators API the same day; this page compares published documents and measured nothing.
- **Primary source:** [Nordic Pure, help center (nominal vs actual size)](https://www.nordicpure.com/nordic-pures-help-center/) (manufacturer or vendor document)
- **Facts verified:** 2026-10-02
- **Last updated:** 2026-10-02
- **Canonical URL (cite this):** https://ownerspec.com/air/parts/furnace-filter-sizes-nominal-vs-actual/

If the frame edge of the filter you just pulled prints an actual size, order that and skip this page: the table below is for the owner who only has the number on the slot, or a media cabinet with no filter left in it.

## What does a nominal size actually measure?

Nordic Pure defines the two terms in one line: nominal size is the rounded number used for labeling, actual size is the true measured dimension, typically slightly smaller, and the gap is an industry standard across air filter brands rather than a defect. Its measuring guide puts the shortfall at 0.25 to 0.5 in and tells an owner measuring a slot to subtract that for clearance.

Only sizes a maker page printed this session carry a number. Filtrete's size chart timed out on every attempt and Nordic Pure's per-size pages for most 1 in filters leave the "Actual Size" field blank, so those rows say so.

| Nominal size | Actual size as the maker prints it | Maker and page |
|---|---|---|
| 14x20x1 | No maker page readable this session; Nordic Pure's rule is 0.25 to 0.5 in under nominal, about 3/4 in thick | Nordic Pure, how to measure |
| 14x25x1 | No maker page readable this session; same rule | Nordic Pure, how to measure |
| 16x20x1 | No maker page readable this session; same rule | Nordic Pure, how to measure |
| 16x25x1 | 15.5 x 24.5 x 0.75 in ("may actually measure") | Nordic Pure, how to measure |
| 20x20x1 | No maker page readable this session; same rule | Nordic Pure, how to measure |
| 20x25x1 | 19 1/2 x 24 1/2 x 3/4 in, may vary up to 1/8 in | Nordic Pure, help center |
| 20x30x1 | No maker page readable this session; same rule | Nordic Pure, how to measure |
| 16x25x2 | No maker page readable this session | Nordic Pure product page lists no actual size |
| 16x25x4 (generic slot) | 15 1/2 x 24 1/2 x 3 5/8 in (15.5 x 24.5 x 3.63) pleated | Nordic Pure, 16x25 nominal sizes |
| 16x25x4 (AprilAire 410) | 16.52 x 29.38 x 4 in | AprilAire, 410 page |
| 16x25x5 | 15 5/8 x 24 1/8 x 4 7/8 (Air Bear), 15 3/4 x 24 3/4 x 4 3/8 (Honeywell/Lennox), 15 3/8 x 25 1/2 x 5 1/4 (Goodman/Carrier/Amana) | Nordic Pure, 16x25 nominal sizes |
| 20x20x4 | 19 1/2 x 19 1/2 x 3 5/8 pleated; 19 5/8 x 19 7/8 x 4 3/8 (Honeywell/Lennox); 19 11/16 x 20 11/16 x 4 15/16 (Air Bear) | Nordic Pure, 20x20 nominal sizes |
| 20x25x4 (generic slot) | 19 1/2 x 24 1/2 x 3 5/8 in (19.5 x 24.5 x 3.63) pleated | Nordic Pure, 20x25x4 actual sizes |
| 20x25x4 (AprilAire 210, 213) | 20.6 x 26.63 x 4 in | AprilAire, 210 and 213 pages |
| 20x25x4 (Honeywell FC200E1037) | 20 x 25 x 4-3/8 in as Resideo prints it; no actual width or height given | Resideo catalog |
| 20x25x5 | 19 3/4 x 24 1/4 x 4 7/8 (Air Bear); 19 3/4 x 24 3/4 x 4 3/8 (Lennox red); 19 7/8 x 24 7/8 x 4 3/8 (Honeywell/Lennox); 20 1/4 x 25 3/8 x 5 1/4 (Goodman/Carrier/Amana) | Nordic Pure, 20x25x5 actual sizes |

A 1 in filter is a commodity: the Filtrete 16x25x1 6 pack and the Filtrete 20x25x1 4 pack drop into any slot of that nominal size. The Amazon Basics 20x25x1 listing title states 19.75 x 24.75 x 0.75 in, a quarter inch over Nordic Pure's figure for the same nominal size: the spread a 1 in slot absorbs and a media cabinet does not.

A 4 or 5 in filter is not a commodity. The same nominal 20x25 is 19.5 in wide for a generic slot and 20.25 in wide for a Goodman, Carrier or Amana cabinet, and Nordic Pure's category pages say in capitals that these filters are specific to actual size. Which MERV to put in the slot is the [MERV, MPR and FPR guide](/air/guides/merv-rating-explained-mpr-fpr/); which brand of 1 in filter is the [furnace filter review](/air/reviews/best-furnace-filter-merv-8-11-13/).

## Which media filter fits which cabinet?

For a cabinet, the model plate decides the part; the makers print the fit list.

| Cabinet | Filter part | Maker's size statement | Rating | Link |
|---|---|---|---|---|
| AprilAire 1210, 1620, 2210, 2216, 3210, 4200; 2120, 2200, Space-Gard 2200 with kit 1213 | AprilAire 210 | Nominal 20H x 25W x 4D, actual 20.6 x 26.63 x 4 in | MERV 11 | AprilAire 210 page; not linked |
| Same cabinets | AprilAire 213 | Nominal 20H x 25W x 4D, actual 20.6 x 26.63 x 4 in | MERV 13 | AprilAire 213, pack of 1 |
| AprilAire 1410, 1610, 2410, 2416, 3410, 4400; 2140, 2400, UV14, UV24 with kit 1413 | AprilAire 410 | Nominal 16H x 25W x 4D, actual 16.52 x 29.38 x 4 in | MERV 11 | AprilAire 410 page; not linked |
| Honeywell 20X25, 25X20, 25X22 F100 and F200; SpaceGard 2200 | FC100A1037/U | 20 x 25 in (508 x 635 mm), depth not printed; 0.23 in w.c. at 500 FPM | MERV 11 | Resideo catalog; not linked |
| Same cabinets | FC200E1037/U | 20 x 25 x 4-3/8 in (508 x 635 x 111 mm); 0.28 in w.c. at 500 FPM | MERV 13 | Resideo catalog; not linked |
| Honeywell F25, F27, F35, F100, F150, F200 at 16x25 | FC100A1029/U | 16 x 25 in; the line also comes in 20x20, 16x20, 21.5x27.5, 20x25 and 20x12.5 | MERV 11 | Resideo pro page; not linked |
| Not stated by Resideo | POPUP1625/U | 16 x 25 x 5 in POPUP media filter | MERV 11 | Resideo pro page; cabinet fit not printed |

The AprilAire 410 is the row to read twice: its label says 16x25x4, its frame is 29.38 in wide, so it will never drop into a 16x25 furnace slot, and a slot filter will never seal in a 2410 cabinet. The Filtrete 16x25x4 4 pack is for the generic slot only; no Filtrete page was readable this session to confirm its actual size, so measure the opening before ordering it.

## How often does a media filter need replacing?

AprilAire prints the interval on all three filter pages: replace the 210, 213 or 410 at least once a year. Resideo's catalog pages for the FC100A1037/U and FC200E1037/U print the pressure drop at 500 FPM but no replacement interval, so the Honeywell figure on this page is a gap rather than a number.

A 1 in filter runs on a shorter clock. The [furnace filter interval guide](/air/guides/how-often-change-furnace-filter/) carries the months each maker prints for 1 in pleats and the condition that shortens each one.

**Which filter to order**

The cheap mistake is the expensive one here: a AprilAire 213 costs more per filter than any 1 in pleat on this page, and it is the only thing that fits a 1210, 2210 or 4200 cabinet, because AprilAire's own page puts it at 20.6 x 26.63 in. If the cabinet plate says 2410 or 4400, skip it and buy the 410 instead.

For a plain slot the Filtrete 16x25x1 MERV 11 6 pack or 20x25x1 4 pack covers several changes at the interval guide's rate. Every listing above was in stock on 2026-10-02.

<!-- FAQ and Sources render from front matter. Do not write them in the body. -->

## The picks

- **Filtrete 16x25x1, MERV 11, MPR 1000 (6 pack)**: Slot takes a nominal 16x25x1 and the old filter came out easily (Listing title: 16x25x1, MERV 11, 6 filters; Nordic Pure's measuring guide puts a 16x25x1 at about 15.5 x 24.5 x 0.75 in actual) Amazon: https://www.amazon.com/dp/B07FP5X3JM/?tag=ownerspec-20
- **Filtrete 20x25x1, MERV 11, MPR 1000 (4 pack)**: Slot takes a nominal 20x25x1 (Listing title: 20x25x1, MERV 11, 4 filters; Nordic Pure's help center puts a 20x25x1 at 19 1/2 x 24 1/2 x 3/4 in actual) Amazon: https://www.amazon.com/dp/B005GZ8C0O/?tag=ownerspec-20
- **Genuine AprilAire 213, MERV 13, 20x25x4 (pack of 1)**: AprilAire cabinet 1210, 1620, 2210, 2216, 3210 or 4200 (AprilAire shop page: nominal 20 x 25 x 4 in, actual 20.6 x 26.63 x 4 in, MERV 13, also fits 2120, 2200 and Space-Gard 2200 with upgrade kit 1213, replace at least once a year) Amazon: https://www.amazon.com/dp/B0040VU3XO/?tag=ownerspec-20
- **Filtrete 16x25x4, MERV 11, MPR 1000 (4 pack)**: Generic 16x25x4 furnace slot, not an AprilAire or Honeywell cabinet (Listing title: 16x25x4, MERV 11, 4 filters; no Filtrete page was readable this session, so measure the slot before ordering a 4 in filter) Amazon: https://www.amazon.com/dp/B01N5GYRTF/?tag=ownerspec-20

## Frequently asked questions

### Can I use a 16x25x1 filter in a 16x25x4 slot?

The slot is about 4 in deep and a 1 in filter is about 3/4 in thick by Nordic Pure's figure, so it will fall over or leave a gap air bypasses. Order the 4 in filter the slot was built for. Nordic Pure lists four actual sizes for a nominal 16x25 media filter, from 3 5/8 to 5 1/4 in deep, so measure the slot depth before choosing one.

### Why is my 20x25x1 filter actually 19 1/2 x 24 1/2?

Nordic Pure's help center says nominal size is the listed, rounded label and actual size is the true measured size, usually slightly smaller, so a filter slides into a slot cut to the nominal number. Its 20x25x1 measures 19 1/2 x 24 1/2 x 3/4 in and may vary up to 1/8 in. Every 1 in filter of the same nominal size is built to the same slot.

### Which AprilAire filter fits a 20x25 cabinet, the 210 or the 213?

Both. AprilAire's shop pages give the 210 (MERV 11) and the 213 (MERV 13) the same actual size, 20.6 x 26.63 x 4 in, and the same cabinet list: 1210, 1620, 2210, 2216, 3210 and 4200 directly, plus 2120, 2200 and Space-Gard 2200 with the 1213 upgrade kit. The choice is the MERV rating, and AprilAire says to replace either at least once a year.

### Does a Honeywell FC100A1037 fit a 20x25x4 furnace slot?

Resideo's catalog lists the FC100A1037/U as a 20 x 25 in MERV 11 filter for Honeywell 20X25, 25X20 and 25X22 F100 and F200 media air cleaners and the SpaceGard 2200, and its MERV 13 twin FC200E1037/U at 20 x 25 x 4-3/8 in. Resideo prints no actual width or height, so a generic 4 in slot is not confirmed by the maker; measure the opening first.


## Sources

- [Nordic Pure, help center (nominal vs actual size)](https://www.nordicpure.com/nordic-pures-help-center/) (manufacturer or vendor document)
- [Nordic Pure, how to measure air filters](https://www.nordicpure.com/how-to-measure/) (manufacturer or vendor document)
- [Nordic Pure, what to know before you buy (nominal and actual size definitions)](https://www.nordicpure.com/is-nordic-pure-a-good-air-filter-what-to-know-before-you-buy/) (manufacturer or vendor document)
- [Nordic Pure, nominal 16x25 media filter actual sizes](https://www.nordicpure.com/shop/ac-furnace-air-filters-2/45-inch/16x25-nominal-sizes/) (manufacturer or vendor document)
- [Nordic Pure, nominal 20x20 media filter actual sizes](https://www.nordicpure.com/shop/ac-furnace-air-filters-2/45-inch/20x20-nominal-sizes/) (manufacturer or vendor document)
- [Nordic Pure, 20x25x4 actual sizes](https://www.nordicpure.com/shop/ac-furnace-air-filters-2/45-inch/20x25x4-actual-sizes/) (manufacturer or vendor document)
- [Nordic Pure, 20x25x5 actual sizes](https://www.nordicpure.com/shop/ac-furnace-air-filters-2/45-inch/20x25x5-actual-sizes/) (manufacturer or vendor document)
- [AprilAire, 213 replacement filter](https://shop.aprilaire.com/products/aprilaire-213-replacement-filter) (manufacturer or vendor document)
- [AprilAire, 210 replacement filter](https://shop.aprilaire.com/products/aprilaire-210-replacement-filter) (manufacturer or vendor document)
- [AprilAire, 410 replacement filter](https://shop.aprilaire.com/products/aprilaire-410-replacement-filter) (manufacturer or vendor document)
- [Resideo customer catalog, FC100A1037/U](https://customer.resideo.com/en-US/Pages/Product.aspx?cat=HonECC+Catalog&pid=FC100A1037%2FU) (manufacturer or vendor document)
- [Resideo customer catalog, FC200E1037/U](https://customer.resideo.com/en-US/Pages/Product.aspx?cat=HonECC+Catalog&pid=FC200E1037%2FU) (manufacturer or vendor document)
- [Resideo, FC100A1029/U 16 x 25 in MERV 11 media filter](https://www.resideo.com/us/en/pro/products/air/air-quality-solutions/filtration/air-cleaner-filters/16-in-x-25-in-merv-11-replacement-media-filter-fc100a1029-u/) (manufacturer or vendor document)
- [Resideo, POPUP1625/U 16 x 25 x 5 in media filter](https://www.resideo.com/us/en/pro/products/air/air-quality-solutions/filtration/air-cleaner-filters/16-in-x-25-in-x-5-in-popup-media-air-filter-popup1625-u/) (manufacturer or vendor document)

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Citation: OwnerSpec, "Furnace Filter Sizes, Nominal vs Actual: What a 16x25x1 Really Measures, and Which 4 in Media Filter Fits an AprilAire or Honeywell Cabinet", https://ownerspec.com/air/parts/furnace-filter-sizes-nominal-vs-actual/, facts verified 2 October 2026.
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