Three numbers compete for space on furnace filter packaging, and only one of them comes from a published industry standard. MERV is defined by ASHRAE. MPR belongs to 3M and appears on Filtrete filters. FPR belongs to The Home Depot and appears on filters it sells.
There is no official conversion between them, and the reason is more interesting than a missing lookup table: the two proprietary systems measure opposite ends of the particle range.
MERV: the one with a standard behind it
MERV runs 1 to 16 and is defined in ASHRAE Standard 52.2, which specifies the test method and the performance required at each level. A filter is rated on its minimum average efficiency across three particle bands — 0.30 to 1.0, 1.0 to 3.0, and 3.0 to 10.0 microns — so a high rating requires competence across the whole range, not just the easy end.
The thresholds are published. MERV 13, the rating the EPA recommends as a minimum for homes, requires at least 50% capture in the finest band, 85% in the middle and 90% in the coarsest. You can look that up, and so can anyone selling you a filter.
One correction worth making, because it still circulates: ASHRAE removed the ratings above 16 from the standard some two decades ago. A claim that a filter is equivalent to “MERV 20” is referring to a rating that no longer exists.
MPR: 3M’s scale, and what it leaves out
MPR stands for Microparticle Performance Rating. It is 3M’s own system, used across the Filtrete range, and the numbers run from about 100 for a basic filter to 2800 for the most efficient.
The critical detail is its scope. MPR rates performance against only the smallest particles, 0.30 to 1.0 microns. It does not report efficiency for larger particles at all — including the 2.5-micron size that PM2.5 limits are built around.
So a high MPR tells you something real and useful about fine particle capture, and nothing whatsoever about pollen, dust mite debris or visible household dust. For a filter that is also protecting your equipment from coarse dust, that is a meaningful gap in the information.
FPR: Home Depot’s scale, weighted the other way
FPR stands for Filter Performance Rating. Home Depot created it for the filters it sells, and it appears as four labeled values: 4 (Good), 7 (Better), 9 (Best) and 10 (Premium).
Behind those labels is an internal score out of 10, weighted 60% on large particles, 30% on small particles and 10% on weight gain over the filter’s life. The particle sizes behind “large” and “small” are not disclosed, and the test method is described only in outline.
That weighting is the mirror image of MPR’s. Where MPR reports only the fine band, FPR gives most of its weight to the coarse end — and then adds a third component, dust-holding capacity, which is not an efficiency measure at all.
Why there is no conversion table
| MERV | MPR | FPR | |
|---|---|---|---|
| Owner | ASHRAE (industry body) | 3M | The Home Depot |
| Range | 1–16 | ~100–2800 | 4, 7, 9, 10 |
| Particles measured | 0.30–10 µm, in three bands | 0.30–1.0 µm only | Undisclosed “large” and “small” |
| Basis of the score | Minimum efficiency in each band | Fine-particle efficiency | 60% large, 30% small, 10% dust held |
| Method published | Yes — ASHRAE 52.2 | No | No, outline only |
Two systems that measure different particle sizes, weight them differently, and include a non-efficiency component in one case cannot be mapped onto each other by a single multiplier. Any conversion chart you find online is someone’s estimate, and the estimate will be wrong in a different direction depending on which particle size you care about.
It is worth noting that both 3M and Home Depot acknowledge MERV as the industry standard. Their own scales exist alongside it, not in place of it.
What to do at the shelf
Look for a MERV number first. Many filters carrying a proprietary rating also print a MERV value, often in smaller type on the side or back of the packaging, or in the online specification list. If it is there, use it and ignore the big number on the front.
If only a proprietary rating is given, treat it as a within-brand ranking. MPR 1900 is more efficient than MPR 1000 from the same manufacturer. That is all it reliably tells you. It does not tell you how either compares with a competitor’s filter, or whether your blower can handle it.
Judge pressure drop separately. None of the three ratings tells you what the filter does to your airflow, and that is the specification most likely to cause a problem. Initial pressure drop, where the manufacturer publishes it, matters more than the rating — particularly in a one-inch slot.
Be suspicious of a rating that implies something off the MERV scale. There is nothing above MERV 16 in the current standard, so an equivalence claim beyond it is not a comparison you can act on.
The underlying point
A proprietary rating is not automatically dishonest, and both of these are measuring something real. But a scale that only its owner can define, test against and interpret is a marketing instrument as much as a specification. It makes comparison within one brand easy and comparison across brands impossible, which is a convenient outcome for whoever owns the scale.
MERV’s value is not that its test is perfect. It is that the test is written down, applies to everyone, and reports the filter’s worst performance rather than its best.
Related guides
- MERV ratings explained, with the full EPA table
- 1-inch vs 4-inch furnace filters
- How often to change a furnace filter
Sources: EPA, What is a MERV rating? for the MERV scale and band thresholds; Energy Vanguard, Understanding Filter Ratings: MERV, FPR, and MPR, for the ownership, ranges, FPR weighting, MPR particle scope, the removal of MERV ratings above 16, and the absence of an official conversion.