AC Filter Sizes Chart: Free Size Finder + Every Standard Size
Measure once, get the exact size to buy. Then the full chart, sizes by HVAC brand, and the MERV rating that actually suits your house.
find your filter size
Measure what you have, or start from your system brand. You'll get the nominal size to buy, the MERV rating that suits your house, and the date your next change is due.
AC filter size chart: every standard size
Every standard air filter size sold for home HVAC systems, with the actual cut size and the depths each one comes in. Furnaces and air handlers take the same sizes, and a furnace and AC on one system share a single filter. Tap any size to load it into the finder above.
swipe the table sideways for 2, 4 and 5 inch sizes
| Nominal size | Actual size (approx) | 1 inch | 2 inch | 4 inch | 5 inch |
|---|---|---|---|---|---|
| 10 × 10 | 9½ × 9½ | 10x10x1 | not common | not common | not common |
| 10 × 20 | 9½ × 19½ | 10x20x1 | 10x20x2 | not common | not common |
| 10 × 24 | 9½ × 23½ | 10x24x1 | not common | not common | not common |
| 10 × 30 | 9½ × 29½ | 10x30x1 | not common | not common | not common |
| 12 × 12 | 11¾ × 11¾ | 12x12x1 | 12x12x2 | not common | not common |
| 12 × 16 | 11½ × 15½ | 12x16x1 | not common | not common | not common |
| 12 × 18 | 11½ × 17½ | 12x18x1 | not common | not common | not common |
| 12 × 20 | 11½ × 19½ | 12x20x1 | 12x20x2 | not common | not common |
| 12 × 24 | 11⅜ × 23⅜ | 12x24x1 | 12x24x2 | 12x24x4 | not common |
| 12 × 25 | 11½ × 24½ | 12x25x1 | 12x25x2 | not common | not common |
| 12 × 30 | 11⅝ × 29½ | 12x30x1 | not common | not common | not common |
| 14 × 14 | 13½ × 13½ | 14x14x1 | not common | not common | not common |
| 14 × 18 | 13½ × 17½ | 14x18x1 | not common | not common | not common |
| 14 × 20 | 13½ × 19½ | 14x20x1 | 14x20x2 | not common | not common |
| 14 × 24 | 13⅜ × 23⅜ | 14x24x1 | not common | not common | not common |
| 14 × 25 | 13½ × 24½ | 14x25x1 | 14x25x2 | not common | not common |
| 14 × 30 | 13½ × 29½ | 14x30x1 | not common | not common | not common |
| 15 × 20 | 14½ × 19½ | 15x20x1 | 15x20x2 | not common | not common |
| 15 × 25 | 14½ × 24½ | 15x25x1 | not common | not common | not common |
| 16 × 16 | 15¾ × 15¾ | 16x16x1 | 16x16x2 | not common | not common |
| 16 × 18 | 15½ × 17½ | 16x18x1 | not common | not common | not common |
| 16 × 20 most common | 15½ × 19½ | 16x20x1 | 16x20x2 | 16x20x4 | 16x20x5 |
| 16 × 24 | 15⅜ × 23⅜ | 16x24x1 | 16x24x2 | not common | not common |
| 16 × 25 most common | 15½ × 24½ | 16x25x1 | 16x25x2 | 16x25x4 | 16x25x5 |
| 16 × 30 | 15½ × 29½ | 16x30x1 | not common | not common | not common |
| 17 × 22 | 16½ × 21½ | 17x22x1 | not common | not common | not common |
| 18 × 18 | 17½ × 17½ | 18x18x1 | 18x18x2 | not common | not common |
| 18 × 20 | 17½ × 19½ | 18x20x1 | 18x20x2 | not common | not common |
| 18 × 22 | 17½ × 21½ | 18x22x1 | not common | not common | not common |
| 18 × 24 | 17⅜ × 23⅜ | 18x24x1 | 18x24x2 | 18x24x4 | not common |
| 18 × 25 | 17½ × 24½ | 18x25x1 | 18x25x2 | not common | not common |
| 18 × 30 | 17½ × 29½ | 18x30x1 | not common | not common | not common |
| 20 × 20 most common | 19½ × 19½ | 20x20x1 | 20x20x2 | 20x20x4 | 20x20x5 |
| 20 × 21 | 19½ × 20½ | 20x21x1 | not common | not common | not common |
| 20 × 22 | 19½ × 21½ | 20x22x1 | not common | not common | not common |
| 20 × 24 | 19⅜ × 23⅜ | 20x24x1 | 20x24x2 | 20x24x4 | not common |
| 20 × 25 most common | 19½ × 24½ | 20x25x1 | 20x25x2 | 20x25x4 | 20x25x5 |
| 20 × 30 | 19½ × 29½ | 20x30x1 | 20x30x2 | not common | not common |
| 22 × 22 | 21½ × 21½ | 22x22x1 | not common | not common | not common |
| 24 × 24 | 23⅜ × 23⅜ | 24x24x1 | 24x24x2 | 24x24x4 | not common |
| 24 × 30 | 23½ × 29½ | 24x30x1 | 24x30x2 | not common | not common |
| 25 × 25 | 24½ × 24½ | 25x25x1 | 25x25x2 | not common | not common |
| 25 × 28 | 24½ × 27½ | not common | 25x28x2 | not common | not common |
| 25 × 29 | 24⅜ × 28⅜ | not common | not common | 25x29x4 | not common |
| 30 × 30 | 29½ × 29½ | 30x30x1 | not common | not common | not common |
| 30 × 36 | 29½ × 35½ | 30x36x1 | 30x36x2 | not common | not common |
Actual sizes are for 1-inch filters and shift by an eighth of an inch or so between makers. 4-inch versions run about ⅛ inch smaller on each side, so a 20x25x4 measures about 19⅜ × 24⅜. A 4-inch filter usually measures about 3⅝ inches deep and a 5-inch about 4⅜. Sizes checked against published filter maker size lists, October 2026. If you're working on a furnace, our furnace filter size guide shows where the size hides on the unit itself.
table of contents
- Filter size finder: measure it, get your size
- AC filter size chart: every standard size
- Nominal vs. actual size: what the numbers mean
- How to find your filter size
- AC filter sizes by HVAC brand
- Filter thickness: 1-inch vs 4-inch
- MERV ratings: which one to choose
- How often to change your AC filter
- Never buy the wrong filter twice
- FAQ
AC filter sizing is confusing because the number on the box isn't the actual size of the filter. It's also confusing because MERV ratings, filter thickness, and dozens of size combinations make the filter aisle at the hardware store feel like a decision tree with no right answer.
This guide covers all of it: what the sizes mean, which ones are most common, how to pick the right MERV rating, and how to make sure you never stand in that aisle guessing again.
Nominal vs. actual size: what the numbers mean
Every filter size is listed as a nominal size, a rounded number that doesn't match the filter's true dimensions. A filter labeled 20x25x1 is actually about 19.5 x 24.5 x 0.75 inches. The undersizing is on purpose. It lets the filter slide in and out of the slot without snagging.
When shopping: always use the nominal size (what's on the box). Never cut a filter to fit. Gaps around the edges let dirty air skip the filter. If the size you need isn't on the shelf, try a filter supply site where custom sizes are often available.
How to find your filter size
Three methods, in order of reliability. (Heating with a furnace? It is the same filter. See what size furnace filter you need for where furnace makers hide the slot and what to buy.)
- Read the existing filter. Pull it out. The nominal size is printed on the cardboard frame. This takes 30 seconds and is 100% accurate.
- Measure the slot. If the filter is missing, use a tape measure: measure the length, width, and depth of the slot opening in inches. Round each dimension up to the nearest standard inch to get the nominal size.
- Check the manual or unit sticker. Your HVAC manual lists the recommended filter size. There's also usually a sticker inside the air handler access panel or on the furnace itself.
AC filter sizes by HVAC brand
HVAC brands don't make filters. They make systems sized to take standard filters. So "Trane filter size" really means "what size filter does my Trane system take?" The answer is almost always one of the same dozen standard sizes above. These are the most common starting points by brand, but always verify by reading the existing filter or measuring the slot.
| HVAC brand | Most common filter sizes | Filter location |
|---|---|---|
| Trane | 16x25x1, 20x25x1, 16x25x4 (XC95m media cabinet) | Return grille or media cabinet at air handler |
| Carrier / Bryant | 16x25x1, 20x25x1, 16x20x1, 20x25x4 (Infinity media cabinet) | Return grille or air handler door |
| Lennox | 16x25x1, 20x25x1, 16x25x5 (Healthy Climate media) | Return grille or PureAir cabinet |
| Goodman / Amana | 16x25x1, 20x25x1, 14x25x1 | Return grille (Goodman systems rarely have media cabinets) |
| Rheem / Ruud | 16x25x1, 20x25x1, 16x20x1 | Return grille or air handler |
| American Standard | 16x25x1, 20x25x1, 16x25x4 (AccuClean media cabinet) | Return grille or media cabinet |
| York / Coleman | 16x25x1, 20x25x1, 16x20x1 | Return grille |
None of these are guaranteed. A 4-ton Carrier system in a small house uses different filters than a 2-ton Carrier in a condo. Use brand as a starting point, then verify with the existing filter, the slot measurement, or the data plate inside the air handler door.
Filter thickness: 1-inch vs 4-inch
Most residential HVAC systems are designed for 1-inch filters. Some newer or upgraded systems have a dedicated media cabinet that accepts 4-inch or 5-inch filters. The thicker filters last longer (6–12 months vs. 1–3 months) and generally filter better because they have more media surface area.
Do not force a 4-inch filter into a slot designed for 1-inch. The increased restriction on airflow can cause the heat exchanger to overheat, increase energy bills, and shorten the life of your system. If you want to upgrade to a thicker filter, have an HVAC technician install the appropriate media cabinet first.
MERV ratings: which one to choose
MERV stands for Minimum Efficiency Reporting Value. It's a scale from 1 to 20 that measures how effectively a filter captures particles of different sizes. Higher = better filtration, but also more airflow resistance.
| MERV rating | What it catches | Best for |
|---|---|---|
| MERV 1–4 | Large dust, pollen, carpet fibers | Window AC units only |
| MERV 8 | Dust, pollen, mold spores, pet dander | Most homes (the standard pick) |
| MERV 11 | All of above + fine dust, smoke particles | Pets, mild allergies |
| MERV 13 | All of above + bacteria, virus carriers | Allergies, asthma, wildfire smoke; the EPA's recommended level if your system handles it |
| MERV 16+ | Near-HEPA filtration | Hospitals and commercial buildings, not homes |
For most homes: MERV 8. If you have pets or allergy sufferers: MERV 11. The EPA recommends MERV 13 or the highest rating your system can take, and says most home systems handle MERV 13 fine if you change it often. The risk is a clogged dense filter, which makes the system work harder, run longer, and cost more to operate. If airflow feels weak after you switch, or your system is old, ask an HVAC tech. And watch the box: Filtrete MPR 1500 is only about MERV 12. For MERV 13, look for MPR 1900.
If the box lists MPR or FPR instead of MERV, the MERV vs MPR vs FPR conversion chart translates it. For a deeper look at which rating your house needs, read what MERV rating you actually need, or skip to our filter picks by rating.
How often to change your AC filter
The standard rule: every 1–3 months for 1-inch filters, every 6–12 months for 4-inch media filters. Those are ranges. Your answer depends on your house:
- Every month: You have multiple pets, someone with severe allergies, or run the system almost continuously
- Every 2 months: One pet, average use, average dust levels
- Every 3 months: No pets, no allergies, moderate use (the typical suburban house)
- Every 6–12 months: 4-inch media filters, low-use vacation homes
A dirty filter doesn't just hurt air quality. It makes your system work harder. Energy bills go up, the system runs longer cycles, and components wear faster. Changing the filter on schedule is the single cheapest thing you can do for HVAC longevity.
Never buy the wrong filter twice
The filter size problem is a solved problem, if you write it down once. Every time someone buys the wrong filter, it's because they didn't record it the last time they changed it.
After your next filter change, add it to kept: size, MERV rating, brand preference, and the date you changed it. The next time you need one, you'll know exactly what to order before you leave the house, and you'll have a record of when it was last changed. If you already keep a home maintenance log, the filter change belongs in it.
kept stores your filter dimensions by unit so reordering takes seconds, not a stepladder.
[ try kept free ]Frequently asked questions
What size AC filter do I need?
Check your current filter. The nominal size is printed on the cardboard frame, for example 20x25x1. If you don't have the old filter, measure the slot opening in inches: length, width and depth. The most common residential sizes are 16x20x1, 20x20x1, 16x25x1 and 20x25x1.
What is the most common AC filter size?
20x25x1 is one of the most common home sizes, along with 16x25x1, 16x20x1 and 20x20x1. Systems with a media cabinet often take a 4-inch filter such as 16x25x4 or 20x25x4. Your system fits only one size, so read the old filter before you buy.
What is the difference between nominal and actual filter size?
Nominal size is the rounded number on the box, like 20x25x1. Actual size is the true measurement, usually about half an inch smaller in length and width, so a 20x25x1 measures about 19.5 x 24.5 x 0.75 inches. Always buy by the nominal size. The slight undersizing lets the filter slide in and out.
How do I know if my AC filter is the right size?
The filter should slide into the slot without bending or forcing, and it shouldn't leave gaps around the edges. A filter that's too loose lets unfiltered air bypass it. A filter you have to force is the wrong size. The arrow on the frame should point toward the blower, not away from it.
Can I use a thicker filter for better air quality?
Only if your system is built for it. Most systems take 1-inch filters. Some have a media cabinet for 4-inch or 5-inch filters, which last longer and filter better. Never force a 4-inch filter into a 1-inch slot. It restricts airflow and can damage your system.