MERV Filter Airflow Calculator
Airflow penalty from a higher MERV filter.
Enter your values
ⓘ Live results
Results
- Face velocity
- 343 FPM
- Estimated filter drop
- 0.244 in wc
- Airflow after filter
- 780 CFM
- Airflow lost
- 35%
- Face area for 300 FPM
- 4 sq ft
Quick answer
Higher MERV filters add resistance, and on a fixed-speed blower each extra 0.1 in wc typically costs 5-10% of airflow.
loss ≈ added drop / rated static x airflow
How to use the MERV Filter Airflow Calculator
- 1Enter measured airflow and the filter's face area in square feet.
- 2Pick the MERV rating you plan to install.
- 3If the loss is over 10%, increase filter area rather than dropping MERV.
Worked example
Using the values the calculator loads with:
Inputs
- Current airflow1200 CFM
- Filter MERVMERV 13
- Filter face area3.5 sq ft
Results
- Face velocity343 FPM
- Estimated filter drop0.244 in wc
- Airflow after filter780 CFM
- Airflow lost35%
- Face area for 300 FPM4 sq ft
Frequently asked questions
Can I run MERV 13 safely?
Yes, if the filter is large enough — a 4-inch deep media cabinet with 4+ sq ft of face area usually works.
Does a dirty filter matter more?
Yes — plan for double the clean pressure drop before the filter is changed.
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.