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Measure Your HVAC Filter Correctly (3-Minute Guide)
Why it matters
A 0.5″ mismatch can cause air bypass and dust leaks. Correct sizing improves filtration and efficiency.
What you need
- Tape measure
- Your current filter (if available)
Steps
1. Power off your system
Slide the filter out carefully.
2. Check the label for nominal size
Look for something like “20x20x1” printed on the frame.
3. If missing, measure actual size
Measure width × height × thickness. Round to the nearest whole number to get the nominal size used when ordering.
Common mistakes to avoid
Swapping width/height
16x25x1 ≠ 25x16x1 on many brands
Forcing a too‑thick filter
Don’t force a 2″ filter into a 1″ slot
Ignoring airflow arrow
Arrow should point toward the blower
What if my size is odd?
Many brands offer custom sizes. Lead times vary; US‑made suppliers often ship custom in days. See custom-size options.
Visual Guide
Width
Height
Thickness
Example: 16″ wide × 25″ tall × 1″ thick = 16x25x1