What Is CFM?
CFM stands for cubic feet per minute. It is a standard unit used to measure airflow and describes how much air moves through a space every minute.
In ventilation design, CFM tells you whether enough fresh or filtered air is being supplied to maintain comfort, control humidity, remove odors, or limit airborne contaminants. Higher CFM values mean more air movement, which generally improves air quality but also increases energy demand.
How the CFM Calculator Works
The calculator determines airflow using room volume and the selected air change rate. Room volume is calculated first, then multiplied by ACH to find how much air must move through the space each hour. That value is converted into cubic feet per minute.
What You Need to Enter
- Room Dimensions: Length, width, and ceiling height are used to calculate total room volume in cubic feet.
- Target ACH: Select or enter the air change rate appropriate for your space and application.
What the CFM Calculator Gives You
- Room Volume: The total amount of air contained in the space.
- Required CFM: The airflow needed to achieve your selected air change rate.
These values provide a starting point for ventilation design and equipment selection.
Example CFM Calculation
Consider a room that is 20 feet long, 15 feet wide, with an 8 foot ceiling. The total volume is 2,400 cubic feet. If the target is 8 air changes per hour, the required airflow would be:
2,400 × 8 ÷ 60 = 320 CFM
This means the ventilation system must move approximately 320 cubic feet of air per minute to meet that requirement.
Understanding Air Changes Per Hour (ACH)
Air changes per hour refers to how many times the full volume of air in a room is replaced within one hour. An ACH of 6 means the room’s air is completely exchanged six times every hour.
ACH requirements vary depending on room use, occupancy, and activities taking place. Spaces with moisture, heat, fumes, or particles typically require higher air change rates.
Common Air Change Rates by Room Type
These values are general guidelines. Local codes, equipment loads, and process requirements may require higher or lower ACH targets.
| Room or Environment | Typical ACH Range |
|---|---|
| Living rooms | 6 to 8 |
| Bedrooms | 5 to 6 |
| Bathrooms | 6 to 10 |
| Kitchens | 7 to 15 |
| Laundry rooms | 8 to 12 |
| Offices | 6 to 8 |
| Conference rooms | 8 to 12 |
| Classrooms | 6 to 20 |
| Retail spaces | 6 to 10 |
| Warehouses | 6 to 10 |
| Laboratories | 6 to 12 |
| Cleanrooms | 10 to 300 |
Why CFM Calculations Matter
Accurately estimating CFM helps prevent poor air quality, excessive humidity, lingering odors, and inefficient HVAC performance. Oversized systems waste energy, while undersized systems fail to properly ventilate the space. A simple CFM calculation ensures airflow aligns with how the space is actually used.
If you need help turning these CFM calculations into a complete air solution, our team can assist you with airflow planning, filter selection, and system recommendations based on your specific space and goals.
