Learn · Air quality
What MERV rating do I need?
For most homes, buy a MERV 11 filter in the size printed on your old one, and change it every 60 to 90 days. Pick MERV 13 for allergies, pets or smoke: the EPA says most home systems can take it if you change it on time. Pick MERV 8 only for an older system or a weak blower.
Find your size to see the lowest price per filter at MERV 8, 11 and 13.
MERV 8 vs 11 vs 13
- MERV 8 — basic dust, lint, pollen. Lowest airflow drag. Good for older systems or anyone chasing maximum airflow.
- MERV 11 — adds fine dust, mold spores, pet dander. The everyday upgrade for most homes.
- MERV 13 — adds smoke, bacteria and most PM2.5. Best for allergies, pets and wildfire smoke — if your system can move air through it (a 1-inch slot usually can; go 4-inch for less restriction).
Different size? Pick your size and see the lowest price per filter at MERV 8, 11 and 13 in the common sizes.
MERV, MPR and FPR — the same thing, three scales
Stores relabel MERV to their own numbers. MPR is 3M/Filtrete’s scale; FPR is Home Depot’s. This is the conversion:
| Tier | MERV | MPR (3M) | FPR (Home Depot) | What it captures |
|---|---|---|---|---|
| Good | 8 | 600 | 5 | Pollen, dust, lint; traps at least 70% of 3-10 micron particles (EPA) |
| Better | 11 | 1000-1200 | 7 | Adds fine dust, mold spores, pet dander; at least 65% of 1-3 micron particles (EPA) |
| Best- | 12 | 1500 | 8-9 | At least 35% of the smallest (0.3-1 micron) particles (EPA) |
| Best | 13 | 1900 | 10 | Adds smoke and bacteria; at least 50% of 0.3-1 micron particles (EPA) |
MPR = 3M/Filtrete proprietary; FPR = Home Depot proprietary (private-label + Honeywell-branded at HD). Neither appears in any central directory. MERV (ASHRAE 52.2) is the only cross-brand standard.
The catch: MERV vs. airflow
Every step up in MERV packs the filter media tighter, so your blower works harder to pull air through it. Push too far on a thin 1-inch filter and you can lose airflow, raise your energy bill, and even ice up the coil. Two safe rules:
- 1-inch slot: MERV 11–13 is the ceiling for most systems. Change it on time — a clogged MERV 8 restricts airflow more than a fresh MERV 13.
- Want MERV 13+ with less drag? Use a 4-inch filter if your system has a deep slot — more surface area means the same filtering with far less restriction, and it lasts 6–12 months.
Find your size
Read the size printed on your current filter — that’s the nominal size. Actual dimensions run about half an inch smaller. Common sizes:
| Nominal size | Actual size | Depth |
|---|---|---|
| 14x25x1 | 13.5 x 24.5 x 0.75 | 1" |
| 16x20x1 | 15.5 x 19.5 x 0.75 | 1" |
| 16x25x1 | 15.5 x 24.5 x 0.75 | 1" |
| 20x20x1 | 19.5 x 19.5 x 0.75 | 1" |
| 20x25x1 | 19.5 x 24.5 x 0.75 | 1" |
| 16x25x4 | 15.375 x 24.375 x 3.625 | 4" |
| 20x25x4 | 19.375 x 24.375 x 3.625 | 4" |
See furnace filters ranked by MERV & yearly cost →
Common questions
What MERV rating is best for a home?
For most homes, MERV 11 to 13 is the sweet spot — it captures fine dust, pollen, mold spores and a good share of smoke and bacteria, without choking airflow on a standard system. Go to MERV 8 if anyone in the home is sensitive to airflow loss or the system is older; go to MERV 13 for allergies, pets or wildfire smoke.
Is a higher MERV always better?
No. A higher MERV traps smaller particles but also restricts airflow more. On a 1-inch filter slot, pushing past MERV 13 can starve the blower, raise energy use and even freeze the coil. Match the MERV to what your system can move — when in doubt, MERV 11–13 in a 1-inch slot, or a thicker 4-inch filter if you want MERV 13+ with less restriction.
What is the difference between MERV, MPR and FPR?
They measure the same thing — how well a filter traps particles — but MERV is the industry ASHRAE standard, MPR is 3M/Filtrete’s own scale, and FPR is Home Depot’s. Use the cross-map on this page to convert: e.g. MERV 13 ≈ MPR 1900 ≈ FPR 10.
How often should I change my furnace filter?
A 1-inch pleated filter every 60–90 days; sooner with pets, smoke or allergies, because they clog faster. A 4-inch filter can last 6–12 months. A clogged filter restricts airflow just like too high a MERV — so changing on time matters as much as the rating you pick.
What size filter do I need?
Read the size printed on your old filter (e.g. 20x25x1) — that is the nominal size. The actual size is about half an inch smaller. Match the nominal size when you buy; the size chart on this page lists the common ones and their true dimensions.
Filter ratings and the MERV/MPR/FPR cross-map are compiled from published manufacturer and retailer specifications (there is no central government filter directory). Written by Erin Rose. See our methodology. We may earn a commission on filter links — it never changes the price or our guidance.