HVAC air filter sizes

Furnace & AC air filter sizes

Find your filter's actual dimensions, how to measure it, and which MERV rating fits your system. Every size page cites EPA, ENERGY STAR and manufacturer specs.

All sizes

10x20x1

10x20x1 air filter

Actual: 9.5 x 19.5 x 0.75 in

1-inch12x12x1

12x12x1 air filter

Actual: 11.75 x 11.75 x 0.75 in (Filterbuy product spec)

1-inch12x24x1

12x24x1 air filter

Actual: 11.5 x 23.5 x 0.75 in (Filterbuy spec; its product text lists 11 3/8 x 23 3/8 x 3/4)

1-inch14x20x1

14x20x1 air filter

Actual: 13.5 x 19.5 x 0.75 in (Filterbuy spec)

1-inch14x24x1

14x24x1 air filter

Actual: 13.38 x 23.38 x 0.75 in

1-inch14x25x1

14x25x1 air filter

Actual: 13.5 x 24.5 x 0.75 in (Filterbuy spec)

1-inch14x30x1

14x30x1 air filter

Actual: 13.88 x 29.88 x 0.75 in (Filterbuy product spec, 13 7/8 x 29 7/8 x 3/4; Filterbuy's general size chart rounds it to 13.5 x 29.5 x 0.75)

1-inch15x20x1

15x20x1 air filter

Actual: 14.5 x 19.5 x 0.75 in (Filterbuy product spec)

1-inch16x16x1

16x16x1 air filter

Actual: 15.75 x 15.75 x 0.75 in (Filterbuy product spec)

1-inch16x20x1

16x20x1 air filter

Actual: 15.5 x 19.5 x 0.75 in (Filterbuy spec)

1-inch16x20x4

16x20x4 air filter

Actual: 15.5 x 19.5 x 3.63 in (Filterbuy spec)

4-inch16x24x1

16x24x1 air filter

Actual: 15.38 x 23.38 x 0.75 in (Filterbuy product spec)

1-inch16x25x1

16x25x1 air filter

Actual: 15.5 x 24.5 x 0.75 in (Filterbuy spec)

1-inch16x25x2

16x25x2 air filter

Actual: 15.5 x 24.5 x 1.75 in

2-inch16x25x4

16x25x4 air filter

Actual: 15.5 x 24.5 x 3.63 in (Filterbuy spec)

4-inch16x25x5

16x25x5 air filter

Actual: 15.75 x 24.75 x 4.38 in (Honeywell/Carrier family; Filterbuy spec, two other cuts exist)

5-inch18x18x1

18x18x1 air filter

Actual: 17.75 x 17.75 x 0.75 in (Filterbuy product spec)

1-inch18x20x1

18x20x1 air filter

Actual: 17.5 x 19.5 x 0.75 in (Filterbuy spec)

1-inch18x24x1

18x24x1 air filter

Actual: 17.38 x 23.38 x 0.75 in (Filterbuy product spec)

1-inch20x20x1

20x20x1 air filter

Actual: 19.5 x 19.5 x 0.75 in (Filterbuy spec)

1-inch20x20x2

20x20x2 air filter

Actual: 19.5 x 19.5 x 1.75 in

2-inch20x20x4

20x20x4 air filter

Actual: 19.5 x 19.5 x 3.63 in (Filterbuy spec)

4-inch20x22x1

20x22x1 air filter

Actual: 19.5 x 21.5 x 0.75 in (Filterbuy spec)

1-inch20x23x1

20x23x1 air filter

Actual: 19.5 x 22.5 x 0.75 in (Filterbuy product spec)

1-inch20x24x1

20x24x1 air filter

Actual: 19.38 x 23.38 x 0.75 in (Filterbuy product spec)

1-inch20x25x1

20x25x1 air filter

Actual: 19.5 x 24.5 x 0.75 in (Filterbuy spec)

1-inch20x25x2

20x25x2 air filter

Actual: 19.5 x 24.5 x 1.75 in

2-inch20x25x4

20x25x4 air filter

Actual: 19.5 x 24.5 x 3.63 in (Filterbuy spec)

4-inch20x25x5

20x25x5 air filter

Actual: 19.88 x 24.75 x 4.38 in (Honeywell/Lennox/Carrier family; Filterbuy spec, two other cuts exist)

5-inch20x30x1

20x30x1 air filter

Actual: 19.63 x 29.63 x 0.75 in (Filterbuy spec; some listings round to 19.5 x 29.5)

1-inch24x24x1

24x24x1 air filter

Actual: 23.38 x 23.38 x 0.75 in (Filterbuy spec)

1-inch25x25x1

25x25x1 air filter

Actual: 24.5 x 24.5 x 0.75 in (Filterbuy product spec)

1-inch

How to measure an air filter

  1. Turn the system off at the thermostat (and the service switch) before pulling the filter.
  2. Read the frame first: the large print is the nominal size (what you order); small print, if present, is the actual size.
  3. If there is no label, measure length, width and depth edge to edge with a tape measure.
  4. Round each measurement up to the nearest whole inch to get the nominal size (e.g. 19.5 x 24.5 x 0.75 → 20x25x1).
  5. No old filter? Measure the filter slot or cabinet opening the same way.
  6. Note the airflow arrow: it should point toward the furnace or blower.

Sizes are written length x width x depth in inches. Filters are cut about 1/4 to 1/2 inch under the nominal size so they fit the slot (Filterbuy, Aerostar).

Choosing MERV

MERVMinimum capture (EPA / ASHRAE 52.2)Good for
8≥20% of 1–3 µm, ≥70% of 3–10 µmBasic dust, pollen, lint; the minimum EPA Indoor airPLUS requires
11≥20% of 0.3–1 µm, ≥65% of 1–3 µm, ≥85% of 3–10 µmA step up for pets and allergies
13≥50% of 0.3–1 µm, ≥85% of 1–3 µm, ≥90% of 3–10 µmEPA's recommended level for fine particles (PM2.5), if your system can accommodate it
⚠ When higher MERV can restrict airflow

EPA notes that higher-MERV filters tend to restrict airflow, and recommends using the highest rating your system fan and filter slot can accommodate. Most systems handle MERV 13 if the filter is replaced frequently. Thin 1-inch slots are the most restrictive; deeper 4-inch media filters generally create less static pressure. Weak airflow from vents, a system that runs longer, or a filter that bows are signs to step down a grade or ask an HVAC technician.

Sources: EPA, EPA Indoor airPLUS, ENERGY STAR, Filterbuy size chart.