HVAC filter sizing guide
Nominal vs. actual HVAC filter size
The size printed on a filter is a nominal catalog label. The physical frame can be smaller, as it is in the reviewed Filtrete examples below. Compare both values before buying, and never force a replacement into the equipment slot.
Page reviewed . The live result route still verifies publication status separately.
Measure in three steps before buying
- Record the nominal label. Copy the existing filter's printed width, height, and depth in the original order. Keep the rating separate from the size.
- Measure the physical frame. With the system safely off, measure the filter itself—not the outer grille or return opening—and retain any fractional or decimal values.
- Compare both values. Open the matching exact size result below and verify that its nominal label and manufacturer-published actual dimensions agree with what you recorded. Do not round a near match or change the orientation.
If the label is unreadable, the slot is damaged, or the old filter appears loose or forced, stop and follow the equipment manual or ask a qualified HVAC professional before purchasing a substitute.
Reviewed two-inch Filtrete examples
| Nominal label | Published actual dimensions | Rating |
|---|---|---|
| 12 × 24 × 2 in | 11.38 × 23.38 × 1.75 in | MPR 700 / MERV 8 |
| 16 × 16 × 2 in | 15.5 × 15.5 × 1.75 in | MPR 700 / MERV 8 |
| 16 × 20 × 2 in | 15.5 × 19.5 × 1.75 in | MPR 700 / MERV 8 |
| 16 × 24 × 2 in | 15.38 × 23.38 × 1.75 in | MPR 700 / MERV 8 |
| 16 × 25 × 2 in | 15.5 × 24.5 × 1.75 in | MPR 700 / MERV 8 |
| 18 × 25 × 2 in | 17.5 × 24.5 × 1.75 in | MPR 700 / MERV 8 |
| 20 × 20 × 2 in | 19.5 × 19.5 × 1.75 in | MPR 700 / MERV 8 |
| 20 × 24 × 2 in | 19.38 × 23.38 × 1.75 in | MPR 700 / MERV 8 |
| 20 × 25 × 2 in | 19.5 × 24.5 × 1.75 in | MPR 700 / MERV 8 |
| 24 × 24 × 2 in | 23.38 × 23.38 × 1.75 in | MPR 700 / MERV 8 |
Physical fit is not system approval
This guide answers only a size and physical-fit question. MERV and MPR describe filtration performance; they do not grant permission to use a filter in a particular system. A dimensional match does not establish acceptable pressure drop, blower capacity, airflow, installation direction, fire-safety compliance, or overall equipment suitability.
Confirm those system-design limits in the equipment manual or with the manufacturer or a qualified HVAC professional. Never infer system suitability solely because a filter physically fits.