CFM Calculator (Cubic Feet per Minute)
Calculate required airflow for rooms and ventilation systems
How to Calculate CFM for Airflow
CFM stands for Cubic Feet per Minute. It is a measurement of the velocity at which air flows into or out of a space. In the context of HVAC (Heating, Ventilation, and Air Conditioning), calculating the CFM is essential to ensure that a room has proper air circulation and quality.
The CFM Formula
To calculate the required CFM for a room based on the desired Air Changes per Hour (ACH), use the following formula:
Step-by-Step Calculation Example
Suppose you have a workshop that is 20 feet long, 15 feet wide, and has 10-foot ceilings. You want to achieve 6 air changes per hour (ACH) to keep the air fresh.
- Calculate Volume: 20ft × 15ft × 10ft = 3,000 Cubic Feet.
- Multiply by ACH: 3,000 × 6 = 18,000 Cubic Feet per hour.
- Convert to Minutes: 18,000 / 60 minutes = 300 CFM.
Recommended Air Changes Per Hour (ACH)
| Room Type | Recommended ACH |
|---|---|
| Living Rooms / Bedrooms | 2 – 4 |
| Kitchens | 6 – 10 |
| Bathrooms | 8 – 12 |
| Garages / Workshops | 6 – 12 |
| Commercial Kitchens | 15 – 30 |
Why is CFM Important?
If your CFM is too low, the air becomes stagnant, allowing moisture, odors, and pollutants to build up. If the CFM is unnecessarily high, you may experience drafts, excessive noise, and higher energy bills due to the HVAC system working harder than required.