Air Filter Size Calculator
Determine the correct HVAC air filter size and replacement schedule for your home.
Choosing the right HVAC air filter is essential for maintaining good indoor air quality, protecting your heating and cooling equipment, and keeping energy costs down. Using the wrong size or type of filter can reduce system efficiency and allow pollutants to circulate in your home.
How to determine your filter size: Air filters are measured by three dimensions: width, height, and depth (thickness). The nominal size (printed on the filter) is rounded to the nearest inch, while the actual size is typically 1/4 to 1/2 inch smaller in each dimension to allow the filter to slide into the filter slot.
Common residential air filter sizes:
- 16×20×1 — One of the most common sizes for smaller HVAC systems
- 16×25×1 — Common in many residential systems
- 20×20×1 — Square format, used in many furnaces
- 20×25×1 — Very popular standard size
- 20×25×4 — Media filter, lasts longer
- 24×24×1 — Common in commercial and larger residential systems
MERV ratings explained: The Minimum Efficiency Reporting Value (MERV) rates a filter’s ability to capture particles. Higher MERV ratings catch smaller particles but also restrict airflow more.
- MERV 1-4: Basic filtration, captures large particles (pollen, dust mites). Minimal allergy protection.
- MERV 5-8: Good residential filtration. Captures mold spores, pet dander, and dust. Suitable for most homes.
- MERV 9-12: Superior residential filtration. Captures fine dust, legionella, and auto emissions. Good for allergy sufferers.
- MERV 13-16: Hospital-grade filtration. Captures bacteria, tobacco smoke, and sneeze droplets. May restrict airflow in some residential systems — check with your HVAC manufacturer.
Replacement schedule:
- 1-inch fiberglass filters: Replace every 30 days
- 1-inch pleated filters: Replace every 60-90 days
- 2-inch pleated filters: Replace every 3-4 months
- 4-inch media filters: Replace every 6-12 months
- 5-inch media filters: Replace every 9-12 months
Factors that shorten filter life: Pets (especially dogs and cats that shed), smokers in the home, nearby construction, high pollen seasons, dusty environments, and running the system continuously.
Energy impact: A dirty filter can increase energy consumption by 5-15% because the HVAC system must work harder to push air through the clogged filter. Regular replacement pays for itself in energy savings.