FilterKey

1″ filters only — the case with one reliable nominal→actual conversion.

No single formula here — the same nominal size differs by brand. Match by brand + model, not nominal size. Use the Whole-House tool above for the shop link, or browse the full whole-house model list.

MERV is the real industry standard (ASHRAE 52.2). FPR and MPR are brand-proprietary scales mapped to it. See the full ratings guide for what each level catches and which one you need.

Prefer to buy the exact line you already use? Browse 1″ filters by brand — Filtrete, Nordic Pure, Filterbuy, Aerostar & AIRx, direct-linked by size and MERV rating.

Dealing with a specific air-quality problem? See the right MERV rating for wildfire smoke or for pet dander & allergies.