Ratings decoder
MPR and MERV Are Not the Same Scale
Two numbers on one filter, published by two different parties, measuring two different things.
The same thing, read twice — Filtrete 20x25x1 MERV 11, 2-pack
What MERV says about it
MERV 11. That places it against every other filter rated by the same ASHRAE test method, from any manufacturer, on a scale that runs to 16.
What MPR says about it
MPR 1000. That places it against other filters from the same manufacturer, on a scale that manufacturer publishes and defines, weighted toward the finest particle range it measures.
Both readings come from the listing for Filtrete 20x25x1 MERV 11, 2-pack, which states: listing states MPR 1000 and an actual size of 19.68 x 24.68 x 0.81 in.
What is actually going on
Walk down a filter aisle and you will see at least three numbering systems competing for the same square inch of packaging. MERV comes from an industry test method. MPR is published by one manufacturer for its own products. FPR is published by one large retailer for the filters it sells. They coexist because each party would rather you compared within its own scheme than across all of them.
MERV is the one that spans manufacturers. It comes from a published ASHRAE test method, so a MERV 11 from one company and a MERV 11 from another have been through the same procedure. That is the entire value of it.
MPR is defined by its publisher and weighted toward the finest particles it measures. It is not wrong, and it is not marketing invented from nothing — it is a real measurement of a real thing. It is simply a different thing, defined by a party with an interest in the outcome, and it produces numbers in the hundreds and thousands where MERV produces numbers under twenty.
The failure mode this causes is straightforward. Someone remembers that their old filter was a 1000, sees a filter labeled 8, concludes the new one is drastically worse, and buys something with far more resistance than the system was specified for. The two numbers were never on the same axis.
The practical rule is short. Compare MERV against MERV and MPR against MPR. Where a filter states both, as several in this catalog do, use whichever scale your reference point is in and ignore the other. And whichever scale you shop in, the equipment documentation still decides what the system can take.
Lined up against each other
| Filter in this catalog | What each scale states for it | Who publishes that number |
|---|---|---|
| Filtrete 20x30x1, MERV 5 | MERV 5 and MPR 300 are both stated on the listing. | MERV from the ASHRAE test method; MPR from the filter manufacturer. |
| Simply 20x20x1, MERV 8 | MERV 8 and MPR 600 are both stated on the listing. | A different manufacturer stating MPR, on the same published scale. |
| Filtrete 20x30x1, MERV 8 | MERV 8 and MPR 700 are both stated on the listing. | Same MERV as the filter above, a different MPR figure. |
| Filtrete 20x25x1, MERV 11 | MERV 11 and MPR 1000 are both stated on the listing. | The pairing that makes the scales look convertible when they are not. |
| Filtrete 20x25x1, MERV 12 | MERV 12 and MPR 1500 are both stated on the listing. | One MERV step, a 500 point MPR step. The intervals do not correspond. |
What this scale does not tell you
- A conversion. There is no arithmetic that turns an MPR figure into a MERV figure or back.
- Which filter a particular system should take — that stays with the equipment documentation.
- Anything about resistance. Neither scale states pressure drop, and both rise with it.
- What a filter without a stated MPR would score, since only the publisher assigns those numbers.