MERV vs MPR vs FPR: why does my filter have three different numbers?

What are MERV, MPR, and FPR?

All three are filter ratings, and all three are trying to tell you the same basic thing: how much of the dust, pollen, dander, and finer stuff in your air a given filter will actually catch. The reason there are three of them is not that they measure different things. It is that one is an open industry standard and the other two are private systems that two big sellers put on their own products.

MERV is the open one. It is set by an independent engineering standards body, it is the number your furnace manual and any HVAC tech will speak in, and it shows up on filters from nearly every brand and store. Because it is independent and tested the same way for everyone, a MERV 11 from one company means the same filtration as a MERV 11 from another. That is the whole value of it.

MPR and FPR are the private ones. MPR belongs to 3M and appears only on its Filtrete line. FPR belongs to The Home Depot and appears on the filters it sells under its own store brands. They are not wrong or fake, they are real ratings, but they are scaled differently from MERV and from each other, and only the company that owns each one uses it. The practical result is the thing that frustrates shoppers: you cannot compare a Filtrete box against a Home Depot box by their printed numbers, because the numbers are written in two different languages. Convert both to MERV and the fog clears.

Who owns each rating: the standard, 3M, and Home Depot

Knowing where each number comes from is what tells you how far to trust it, so here is the short ownership story for all three.

MERV stands for Minimum Efficiency Reporting Value, and it is defined by ANSI/ASHRAE Standard 52.2, the method the heating and cooling engineering society publishes for testing air filters. It grades a filter across the full range of particle sizes a home cares about, roughly 0.3 to 10 microns, which covers everything from fine smoke particles up to visible dust and pollen. The residential scale runs about 1 to 16; some charts stretch it to 20, but 17 and up are HEPA-class filters for clean rooms and hospitals, not something a normal furnace runs. The point is that MERV is set by an outside body, not by a company selling filters, and that is why it is the number that means the same thing everywhere. The Environmental Protection Agency, when it gives filtration advice, speaks in MERV.

MPR stands for Microparticle Performance Rating, and it is 3M's own scale for its Filtrete filters. Its numbers run from a few hundred up to about 2,800, which is why an MPR number looks so much bigger than a MERV number. There is a catch worth knowing: MPR rates only how well a filter grabs the very smallest particles, the 0.3 to 1 micron range. That is a real and useful thing to measure, but it means MPR does not score the larger particles that MERV's broader test still counts. So a high MPR tells you a filter is good at the tiniest stuff specifically, not that it is the best overall filter for a typical home. MPR is genuinely handy for one job: comparing one Filtrete filter to another. Across brands it does not translate.

FPR stands for Filter Performance Rating, and it is Home Depot's own scale, on a 4 to 10 range, used on the filters it sells under brands like Honeywell Home and HDX. It rolls a filter's capture, its dust capacity, and its airflow into one color-coded good, better, best, and premium set of tiers, which is handy for picking a level off the Home Depot shelf. The trade-off is that bundling everything into one coarse number hides the detail, and FPR has no published particle-size basis, which makes it the hardest of the three to convert reliably to anything else.

MERV to MPR to FPR conversion chart

This is the table everyone comes looking for, so here it is, anchored to MERV because MERV is the one all three can be lined up against. Read it as approximate. No one publishes an official cross-map, the test methods differ, and as you will see in the next section, the same filter can land a step or two apart depending on who is doing the rating.

A couple of notes on the edges of that chart. 3M's own paperwork pairs MPR 600 with MERV 7 rather than 8, so the first row is the soft one; call it roughly MERV 7 to 8. And the top of the MPR scale, the 2,500 and 2,800 filters, lands around MERV 14 by 3M's own numbers, not MERV 13, so do not assume the biggest MPR on the shelf is a MERV 13. If you only remember one thing from the table, remember the middle rows: MERV 11 is about MPR 1000 to 1200 and FPR 7, and MERV 13 is about MPR 1900 and FPR 10.

Is MPR 1000 the same as MERV 8, and why isn't the chart exact?

Close, but this is exactly where people get tripped up, so it is worth being precise. MPR 1000 is closer to MERV 11 than MERV 8. MPR 600 is the one near MERV 8, and even that one 3M lists as MERV 7. The bigger point is why none of these conversions is a clean equals sign.

The systems were built on different tests. MERV grades a filter across a wide band of particle sizes; MPR scores only the tiniest particles; FPR mixes capture, dust capacity, and airflow into one number with no published particle-size definition at all. Three different yardsticks measuring three slightly different things will never line up perfectly, and on top of that, the private ratings are self-reported by their owners with no outside lab checking them.

FPR is the loosest of the three, and Home Depot's own catalog proves it. The same FPR 9 shows up on one of its filters as MERV 11 and on another as MERV 13. An FPR 10 filter turns up as MERV 12 on one product while charts elsewhere call FPR 10 a MERV 13. So an FPR number does not even map to a single MERV inside Home Depot's own aisle, let alone across stores. Treat FPR as a rough band, not a precise dial, and when in doubt, find the MERV.

How to find the real MERV number on a Filtrete or Home Depot box

The good news is that most boxes already print the MERV, just not in the big type. You usually do not have to convert anything; you have to look harder at the package you are holding.

On a Filtrete box, the headline number is the MPR, but the MERV is almost always there too, often on a side or back panel or in the product title online, listed as something like MERV 12 next to MPR 1500. Home Depot's own store-brand filters are even more direct: the listing usually prints both, such as FPR 9 and MERV 13, right in the product name. So step one is simply to scan the box and the online listing for the letters M-E-R-V before you reach for any chart.

If the MERV genuinely is not printed anywhere, then use the conversion chart above to estimate it, leaning on the reliable middle rows. And if you shop a store that leads with MERV already, which most do outside of Home Depot and the Filtrete shelf, you can skip all of this and just read the number off the box. The whole trick is to make MERV the number you decide on, and let MPR and FPR be things you translate, not things you trust on their own.

Which number should you actually trust?

MERV, without much of a contest. It is the only one of the three set by an outside standards body rather than by a company that wants to sell you its filter, it is the only one your equipment manufacturer specifies, and it is the only one you can carry from store to store and brand to brand and have it mean the same thing. MPR and FPR are fine for navigating within the one store or brand that uses them, but the moment you want to compare across the aisle or across stores, you have to come back to MERV.

One caution that applies to all three scales equally: a bigger number is not automatically a better buy. A higher MERV, MPR, or FPR means denser filter media, and denser media restricts airflow and clogs sooner, so a higher-rated filter also tends to need changing more often. On some systems, especially older furnaces or homes with undersized return ducts, pushing the rating too high makes the blower work harder and can cost you in energy and wear. So the highest number on the shelf is not the safe default, on any of the three rulers. Whether your system can handle a higher-rated filter is its own question, and our guide to choosing between MERV 8, 11, and 13 covers which level fits common households and whether your furnace can take a MERV 13.

Quick answers on MERV, MPR, and FPR

A few more questions that come up when people compare filter ratings.

Are MERV, MPR, and FPR interchangeable? They describe the same idea but are not interchangeable numbers, because each uses a different scale and a different test. MERV is the only one that translates across brands.

Is a higher MPR better than a high MERV? Not necessarily. MPR only measures the smallest particles, so a large MPR means strong fine-particle capture, not better overall filtration than a comparable MERV. Match them through the chart rather than comparing the raw numbers.

Which rating does a furnace or HEPA use? Furnaces and the pros who service them use MERV. HEPA is a separate, much higher class of filtration that sits above the normal MERV range and is not what a standard furnace filter slot is built for.

So which filter should I actually buy? Once you have decided to shop by MERV, the next question is which MERV level your home and your system call for, and that is its own decision. Our MERV filter selector walks you to the right level for your situation.