Free Tool
Free HVAC CFM calculator
Enter a room's size and air changes per hour to get the required airflow in CFM. A quick rule-of-thumb for balancing registers. Free, no signup.
Set by room type; override if you have a target
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Airflow a room actually needs
CFM is cubic feet per minute, the airflow a room needs to feel right. The math is the room's volume times how many times you want to change its air each hour, divided by 60 to get per minute.
Air changes vary by room. A bedroom is comfortable with fewer; a kitchen or bath needs more to clear heat, steam, and odors. Pick the room type and the calculator sets a typical air-change rate, or you can enter your own target.
Use this to sanity-check a room and balance the registers, not to size the system. Equipment sizing comes from a Manual J load calculation that accounts for the whole house, insulation, windows, orientation, and climate, and that belongs with a licensed HVAC pro.
Add up the room CFMs and you get a feel for the total the system moves, which is a useful gut check against the equipment already in place.
HVAC CFM Calculator questions
How do you calculate CFM for a room?
Multiply the room's volume (length × width × ceiling height) by the air changes per hour, then divide by 60. The calculator does it for you.
What are air changes per hour?
How many times the room's full air volume is replaced each hour. Bedrooms need fewer; kitchens and baths need more.
Does this size my furnace or AC?
No. This is a room rule-of-thumb. Equipment sizing needs a Manual J load calculation from a licensed HVAC pro.
Is this really free?
Yes. No email, no signup, and nothing you type leaves your browser.
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Disclaimer: These free tools and templates are provided for general information and estimating purposes only. All results — including quantities, material and cost estimates, load, sizing, and span figures, scores, and any guidance or warnings — are rough approximations that may not fit your specific project, site conditions, local building codes, or current prices. They are not engineering, architectural, structural, legal, financial, or other professional advice, and are not a substitute for a licensed engineer, architect, contractor, or other qualified professional. Always confirm quantities, sizing, and structural, electrical, mechanical, and code requirements with a licensed professional and your local authority having jurisdiction before purchasing materials or performing any work. Werx makes no warranty as to accuracy and accepts no liability for any decision made using these tools. Use at your own risk. See our Terms of Service.