Carbon Filter CFM Calculator
Match filter rating to fan and check contact time.
Enter your values
ⓘ Live results
Results
- 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)
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.
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.
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.