How to read filter size

What to read

1. Pull the existing filter (power off the blower if your system requires it).
2. Find the size string on the cardboard edge — usually W × L × T in inches.
3. Match all three numbers. Thickness errors are the most common return reason.

Nominal vs actual

Many filters are labeled with a nominal size (e.g. 16×25×1) while the cardboard is a fraction smaller so it slides into the slot. Order by the labeled size your old filter shows, not a tape measure of the media alone.

Size ≠ grade

MERV / Filtrete MPR describes capture efficiency, not fit. A higher grade in the wrong thickness still does not fit. Grade notes: Filtrete MERV guide.

Cabinet limits

Some OEM media cabinets only accept a specific thickness. If the blower door or media cabinet lists a required size, that wins over a retail “universal” claim.

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