Carbon Filter CFM Calculator
Match filter rating to fan and check contact time.
Enter your values
Enter the fan rating in CFM.
Enter the filter rating in CFM.
Enter the filter pressure loss in %.
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.
- Delivered airflow
- 300 CFM
- Filter headroom
- 0%
- Match verdict
- Filter is correctly matched or oversized
- Recommended filter
- 500 CFM
Quick answer
A carbon filter should be rated at or above the fan's CFM; running a fan flat out through an undersized filter destroys odour control.
delivered CFM = fan CFM x (1 − filter loss)
At a glance
| What it does | Match filter rating to fan and check contact time. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Fan rating, Filter rating, Filter pressure loss |
| Main output | Delivered airflow |
| Formula | delivered CFM = fan CFM x (1 − filter loss) |
| Cost | Free — no sign-up, no download |
How to use the Carbon Filter CFM Calculator
- 1Enter your fan's rated CFM and the filter's rating.
- 2Set a realistic pressure loss — 20–25% for a new filter, more as it loads.
- 3Buy a filter rated 20% above the fan for a long service life.
Inputs explained
- Fan rating(CFM)
- Enter the fan rating in CFM.
- Filter rating(CFM)
- Enter the filter rating in CFM.
- Filter pressure loss(%)
- Enter the filter pressure loss in %.
Worked example
Using the values the calculator loads with:
Inputs
- Fan rating400 CFM
- Filter rating400 CFM
- Filter pressure loss25 %
Results
- Delivered airflow300 CFM
- Filter headroom0%
- Match verdictFilter is correctly matched or oversized
- Recommended filter500 CFM
Frequently asked questions
Can a filter be too big?
No. An oversized filter has lower face velocity, longer contact time and lasts longer.
How long does carbon last?
Typically 12–18 months of continuous use, less in humid air.
What do I need to enter into the Carbon Filter CFM Calculator?
Just 3 values: fan rating, filter rating, filter pressure loss. 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 Carbon Filter CFM Calculator work out the answer?
A carbon filter should be rated at or above the fan's CFM; running a fan flat out through an undersized filter destroys odour control. It applies the formula delivered CFM = fan CFM x (1 − filter loss) and shows the working so you can check each step by hand.
Is the Carbon Filter CFM 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.