Filter Grille Size Calculator
Size a return filter grille for low pressure drop.
Enter your values
ⓘ Live results
Results
- Required filter area
- 2.67 sq ft
- Approx square filter size
- 19.6 x 19.6 in
- 20x25 filters needed
- 0.8 filters
- 20x20 filters needed
- 1 filters
Quick answer
Filter grilles are sized for a lower face velocity than plain return grilles, typically 250-350 FPM, because the filter media adds resistance.
Filter area = return CFM / face velocity
How to use the Filter Grille Size Calculator
- 1Enter the total return CFM that will pass through the filter grille.
- 2Use 250-300 FPM face velocity for a MERV 8-13 filter to control pressure drop.
- 3Compare against common filter sizes to see how many grilles or how large a single grille needs to be.
Worked example
Using the values the calculator loads with:
Inputs
- Return airflow800 CFM
- Filter face velocity300 FPM
Results
- Required filter area2.67 sq ft
- Approx square filter size19.6 x 19.6 in
- 20x25 filters needed0.8 filters
- 20x20 filters needed1 filters
Frequently asked questions
Why lower velocity than a plain grille?
Filter media adds resistance, so lower face velocity keeps total static pressure and noise reasonable.
What if my filter grille is undersized?
It raises static pressure, cuts airflow and shortens filter life due to higher loading per square inch.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.