HEPA Filter Airflow Calculator
Face velocity and airflow for a HEPA filter.
Enter your values
Enter the filter width in in.
Enter the filter height in in.
Enter the face velocity in FPM.
Enter the rated clean drop in in wc.
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.
- Airflow
- 1,000 CFM
- Face area
- 4 sq ft
- Estimated pressure drop
- 1 in wc
- Change-out drop (2x)
- 2 in wc
- In m³/h
- 1,699
Quick answer
HEPA filters are rated near 250-500 FPM face velocity; going higher pushes pressure drop up steeply.
CFM = face area (sq ft) x face velocity
At a glance
| What it does | Face velocity and airflow for a HEPA filter. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Filter width, Filter height, Face velocity, Rated clean drop |
| Main output | Airflow |
| Formula | CFM = face area (sq ft) x face velocity |
| Cost | Free — no sign-up, no download |
How to use the HEPA Filter Airflow Calculator
- 1Enter the filter panel dimensions and target face velocity.
- 2Check the pressure drop against the fan's available static.
- 3Replace at roughly double the clean pressure drop.
Inputs explained
- Filter width(in)
- Enter the filter width in in.
- Filter height(in)
- Enter the filter height in in.
- Face velocity(FPM)
- Enter the face velocity in FPM.
- Rated clean drop(in wc)
- Enter the rated clean drop in in wc.
Worked example
Using the values the calculator loads with:
Inputs
- Filter width24 in
- Filter height24 in
- Face velocity250 FPM
- Rated clean drop1.0 in wc
Results
- Airflow1,000 CFM
- Face area4 sq ft
- Estimated pressure drop1 in wc
- Change-out drop (2x)2 in wc
- In m³/h1,699
Frequently asked questions
Can HEPA go in a home furnace?
Only with a purpose-built bypass cabinet and booster fan — a standard blower cannot overcome the drop.
True HEPA?
99.97% capture at 0.3 microns; anything labelled HEPA-type is not certified.
What do I need to enter into the HEPA Filter Airflow Calculator?
Just 4 values: filter width, filter height, face velocity, rated clean drop. 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 HEPA Filter Airflow Calculator work out the answer?
HEPA filters are rated near 250-500 FPM face velocity; going higher pushes pressure drop up steeply. It applies the formula CFM = face area (sq ft) x face velocity and shows the working so you can check each step by hand.
Is the HEPA 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.