MERV Filter Airflow Calculator
Airflow penalty from a higher MERV filter.
Enter your values
Enter the current airflow in CFM.
Choose one of: MERV 8, MERV 11, MERV 13, MERV 16.
Enter the filter face area in sq ft.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Airflow penalty from a higher MERV filter. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Current airflow, Filter MERV, Filter face area |
| Main output | Face velocity |
| Formula | loss ≈ added drop / rated static x airflow |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Current airflow(CFM)
- Enter the current airflow in CFM.
- Filter MERV
- Choose one of: MERV 8, MERV 11, MERV 13, MERV 16.
- Filter face area(sq ft)
- Enter the filter face area in sq ft.
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.
What do I need to enter into the MERV Filter Airflow Calculator?
Just 3 values: current airflow, filter merv, filter face area. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the MERV Filter Airflow Calculator work out the answer?
Higher MERV filters add resistance, and on a fixed-speed blower each extra 0.1 in wc typically costs 5-10% of airflow. It applies the formula loss ≈ added drop / rated static x airflow and shows the working so you can check each step by hand.
Is the MERV Filter Airflow Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.