Full size chart
1″ filters only — the case with one reliable nominal→actual conversion.
| Nominal | Actual dimensions | Notes |
|---|
4″ / 5″ whole-house filters
No single formula here — the same nominal size differs by brand. Match by model number, not nominal size.
Full rating chart
MERV is the real industry standard (ASHRAE 52.2). FPR and MPR are brand-proprietary scales mapped to it.