Look for the "nominal size" (e.g., 20x25x1) printed on the edge of your current filter.
When buying central air conditioning filters, you must balance air filtration quality with your system's airflow requirements to avoid equipment damage. 1. Find Your Filter Size
If the label is missing, measure the length, width, and thickness of the filter slot. Round up to the nearest whole inch to find the nominal size.
Size is the most critical factor; an ill-fitting filter allows unfiltered air to bypass the system.
The Minimum Efficiency Reporting Value (MERV) scale (1–16) measures how well a filter captures particles. What is a MERV rating? | US EPA
Residential filters are typically 1 inch thick, but high-efficiency systems may use 4- or 5-inch filters. 2. Choose the Right MERV Rating
