CFM Airflow Calculator

About the CFM Airflow Calculator

Calculates the airflow in cubic feet per minute (CFM) needed to achieve a target number of air changes per hour (ACH) for a room.

How to use this calculator

1. Enter the room volume in cubic feet, or find it by multiplying length, width, and height.
2. Enter the desired air changes per hour, or ACH.
3. Click calculate to get the required airflow in CFM.
4. Use the result to compare ventilation needs for a room, duct, or fan setup.

The formula explained

The formula CFM = \frac{volume \times ACH}{60} computes the airflow needed in cubic feet per minute. It converts air changes per hour into air changes per minute by dividing by 60.

• CFM = the required airflow in cubic feet per minute
• volume = the room volume in cubic feet
• ACH = air changes per hour

Step by step method

1. Find the room volume using volume = length \times width \times height, if it is not already known.
2. Multiply the volume by the desired ACH.
3. Divide by 60 to convert the hourly rate into a per-minute airflow requirement.

Worked example

Problem. A room has a volume of 1800 cubic feet and needs 6 air changes per hour. Find the required airflow.

1. Use the formula CFM = \frac{volume \times ACH}{60}.
2. Substitute the values, CFM = \frac{1800 \times 6}{60}, which gives 180.
3. So the required airflow is 180 cubic feet per minute.

Tips and common mistakes

• Make sure the volume is in cubic feet before using the formula, not square feet.
• A higher ACH means more ventilation, but it also means a higher CFM requirement.

Frequently asked questions