Ventilation Fan CFM Calculator

What Is a Ventilation Fan Calculator?

A Ventilation Fan CFM Calculator is a tool that helps you determine the correct size (in CFM) for an exhaust fan based on the type of room and its dimensions. Proper fan sizing is critical for effectively controlling moisture, odors, and indoor air pollutants. This is essential for maintaining good indoor air quality and protecting your home's structure from moisture damage. Our free calculator provides an instant, accurate recommendation.

Last updated: November 8, 2025

How to Use This Calculator

Our free CFM calculator provides an accurate fan size in seconds. Follow these steps:

1. Select Room Type: Choose the room where the fan will be installed (e.g., Bathroom, Kitchen).
2. Enter Room Dimensions: Input the length, width, and height of the room in feet.
3. Specify Occupants (for Whole-House): If calculating for a whole-house system, enter the number of people living in the home.
4. Click "Calculate CFM": Get an instant recommendation for the required fan airflow capacity.

Understanding Your Ventilation Fan Calculation

The calculator provides two key pieces of information to help you select the right fan for your needs.

• Recommended Airflow (CFM): This is the minimum airflow capacity your fan should have to properly ventilate the space. Choosing a fan with at least this CFM rating is essential for good performance.
• Suggested Fan/Duct Size: This provides a common duct diameter associated with the required CFM. Most residential fans use 4-inch or 6-inch ducts. A larger duct allows for quieter operation and better airflow.

According to the Home Ventilating Institute (HVI), proper mechanical ventilation is necessary in modern, tightly-sealed homes to ensure a healthy indoor environment by exhausting pollutants and moisture.

Example CFM Calculation (Bathroom)

Here is a common scenario for sizing a bathroom exhaust fan.

Frequently Asked Questions