What is CFM?
CFM (Cubic Feet per Minute) measures the volume of air an air purifier can move. This calculator helps you determine the CFM needed to achieve your desired number of air changes per hour (ACH).
Enter Room Dimensions
Required CFM
Room Volume
0 cu ft
Required CFM
0 CFM
How CFM is Calculated
CFM is calculated by dividing the room volume by 60 minutes, then multiplying by desired air changes per hour.
CFM = (Room Volume x Air Changes) / 60
- 1 Calculate room volume: Length x Width x Height
- 2 Choose desired air changes per hour (ACH)
- 3 Multiply volume by ACH
- 4 Divide by 60 to convert to per-minute rate
CFM Tips
4 ACH is standard for most residential spaces
6+ ACH recommended for allergy and asthma sufferers
Higher ceilings require more CFM for same ACH
CFM ratings are usually at highest fan speed
CFM FAQ
What's the difference between CFM and CADR?
CFM measures total airflow volume, while CADR measures how much clean air is delivered after filtering. CADR is always lower than CFM because not all air passing through is fully filtered.
How many air changes per hour do I need?
2-4 ACH for general use, 5-6 ACH for allergies or pets, 6-8 ACH for smoke or heavy pollution. Medical guidelines often recommend 6+ ACH for virus mitigation.
Does running on low speed affect CFM?
Yes, CFM ratings are typically at maximum speed. Low and medium settings significantly reduce actual CFM and air changes per hour.