HVAC CFM Calculator
Use our free CFM calculator to find the right airflow for any room based on its size and ventilation needs. Enter the square footage and desired air changes per hour (ACH) to get a clear CFM value.
This helps HVAC technicians size systems correctly, avoid energy waste, and deliver consistent comfort across different room sizes.
Disclaimer:
The outputs, any associated images or diagrams, any measurements, and any and all other information (collectively, the “Outputs”) are provided for informational purposes only and do not constitute a binding quote or professional advice. The Outputs are based on general assumptions and the information you provided, which may not reflect the actual specifications or condition of the subject of the calculation, particularly in the case of complex structures or inputs. Accuracy may also vary depending on location, as some data may be more complete in certain regions than others. Actual results or outcomes may vary significantly following an onsite inspection and detailed assessment by a qualified professional. Any auto-generated visuals are for illustrative purposes and may not accurately represent the subject of the calculation. The Outputs should not be relied upon as a final result or used as the sole basis for financial, renovation, operational, or strategic decisions. Jobber recommends consultation with a qualified professional before proceeding with any work, quotes, or financial decisions. Jobber and its affiliates make no warranties, express or implied, regarding the accuracy, completeness, or suitability of the Outputs, and to the fullest extent permitted by law, we disclaim all liability for any damages or losses arising from reliance on the Outputs.
How to use our CFM calculator
To calculate CFM for room airflow needs, HVAC contractors use CFM to measure how much air moves through a room. Our CFM room calculator makes it easy to determine the required CFM based on room dimensions and desired air changes per hour (ACH).
Just enter the required details below:
- Desired ACH, usually entered as a whole number
- Room volume (in cubic feet) or room dimensions (length, width, height)
If you already know the room volume, just multiply it by the ACH and divide by 60. If not, the calculator will use the room’s dimensions to determine the air volume for you.
Once you’ve entered your values, click the “Calculate” button to view the results.
Below is an example of how you can use our calculator to find the CFM of a room measuring 15×20 with standard 8-foot ceilings and 2 ACH:
Enter the following values into the CFM ventilation calculator. You can use a unit converter if your measurements are in different formats, such as meters or inches:
- Air changes per hour: 2
- Room length (feet): 15
- Room width (feet): 20
- Room height (feet): 8
This gives us a required airflow rate of 80 CFM.
How to calculate CFM for a room
To calculate cubic feet per minute, you need to know the size of the space and the number of desired air changes per hour (ACH). You can calculate CFM using this formula:
CFM = (Room Volume × ACH) ÷ 60
Let’s break that down step by step:
- Calculate the room volume (length x width x height) in feet. You can round up if needed.
- Determine ACH, which is the target air change number per hour.
- Multiply room volume by ACH.
- Divide by 60 to convert hours to minutes.
For example, let’s say you’re calculating CFM for a bedroom that’s 15 feet long and 18 feet wide with a ceiling height of 9 feet. Here’s how we would complete the calculation:
- Calculate room volume: 2,430 cubic feet (15’ x 18’ x 9’)
- Determine ACH: 5 (common for offices and bedrooms)
- Multiply room volume by ACH: 12,150 (2,430 x 5)
- Divide by 60: 202.5 CFM
This is just one example of a basic HVAC CFM calculation that helps balance airflow in a space. For quick and easy reference, you can also use the CFM chart below to get airflow for different room sizes:
| Room Volume | CFM (At 2 ACH) |
| 1,000 ft3 | 33.3 CFM |
| 1,500 ft3 | 50 CFM |
| 2,000 ft3 | 66.6 CFM |
| 2,500 ft3 | 83.3 CFM |
| 3,000 ft3 | 100 CFM |
| 3,500 ft3 | 116.6 CFM |
| 4,000 ft3 | 133.3 CFM |
| 4,500 ft3 | 150 CFM |
| 5,000 ft3 | 166.6 CFM |
This CFM airflow guide gives HVAC professionals a quick way to estimate room CFM values. For more precise work, they may also reference duct dimensions and volume flow data.
Frequently Asked Questions
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HVAC CFM calculators are mostly used by contractors, HVAC engineers, and system designers who need quick, accurate airflow estimates. They’re often included in HVAC apps.
These valuable HVAC tools help make sure the system moves the right amount of air for the space, which improves air quality and overall energy efficiency.
Anyone who needs to match airflow to a room size, load requirement, or code spec can benefit from a CFM calculator. Common users include:
• HVAC installers size ducts, registers, or fans during new installs.
• Service techs troubleshoot low airflow or verify system performance.
• Design engineers plan out systems for commercial or residential jobs.
• Home energy auditors calculate air changes per hour and ventilation needs.
• Facility managers check airflow for maintenance or compliance reasons.
CFM calculators are also helpful for anyone conducting an HVAC inspection, doing an HVAC installation, or running an HVAC business.
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To calculate CFM per square foot, divide the total airflow in CFM by the area of the space in square feet. Here’s the basic formula to determine CFM:
CFM per square foot = Total CFM ÷ Room Area (sq ft)
For example, if a room is 300 square feet and receives 600 CFM of airflow, the total CFM per square foot can be calculated as follows:
600 CFM ÷ 300 sq ft = 2 CFM per sq ft
This helps check if a space is getting proper airflow for comfort or indoor air quality. For example, general-purpose rooms often need 1–2 CFM per square foot, but high-use areas like kitchens, gyms, or server rooms could need more.
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CFM (cubic feet per minute) and ACH (air changes per hour) both measure airflow—but in different ways:
• CFM is airflow rate. It tells you how much air is moving through a system every minute. It’s a real-time measure of volume—how fast air is flowing. It helps you size ducts, fans, and vents.
• ACH is the air exchange rate. It tells you how many times the air in a room is replaced in an hour. It’s based on the total volume of the space and the airflow rate. This helps you check if a space has enough ventilation. -
The amount of ACH (air changes per hour) needed will vary depending on the room type and how enclosed the space is. Rooms with more moisture, odors, or pollutants—like kitchens and bathrooms—require more ACH than living rooms or bedrooms.
You can use this quick reference guide for recommended ACH in different rooms:
• Living room: 3–4 ACH
• Bedroom: 5–6 ACH
• Kitchen: 7–8 ACH
• Bathroom: 7–8 ACH
• Laundry room: 8–9 ACH
• Attic: 12–15 ACH
• Garage: 20–30 ACH
Recommended ACH also depends on the desired air quality. The higher the air circulation, the better the air quality will be.
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The amount of airflow a room needs depends on its size, use, and ventilation standards. Most HVAC pros use local codes or ASHRAE recommendations to figure it out.
For quick calculations, use the HVAC CFM calculation formula for rooms with standard 8-foot ceilings: CFM = Room Area (sq ft) × 1–2
Here are some typical airflow requirements, which can ensure systems like a heat pump or air conditioner aren’t over- or under-sized:
• Living room: 1–2 CFM/sq ft
• Bedroom: 1–2 CFM/sq ft
• Kitchen: 2–3+ CFM/sq ft
• Bathroom: 50–100+ CFM total
• Office: 1–2 CFM/sq ft
If you’re designing for air quality or code compliance in commercial settings, healthcare, or high-performance homes, calculate based on ACH using the CFM formula: CFM = (Room Volume × ACH) ÷ 60
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