Room CFM Calculator
Supply CFM a room needs from its square footage.
Enter your values
Enter the system airflow in CFM.
Enter the conditioned floor area in sq ft.
Enter the room area in sq ft.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Room supply airflow
- 120 CFM
- CFM per sq ft
- 0.67
- Share of system
- 10%
- Suggested register count
- 1
Working
- 11,200 CFM x 180 / 1,800 = 120 CFM
Quick answer
Room airflow is normally allocated in proportion to floor area, at roughly 1 CFM per square foot for typical residential systems.
room CFM = total CFM x room area / house area
At a glance
| What it does | Supply CFM a room needs from its square footage. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | System airflow, Conditioned floor area, Room area |
| Main output | Room supply airflow |
| Formula | room CFM = total CFM x room area / house area |
| Cost | Free — no sign-up, no download |
How to use the Room CFM Calculator
- 1Enter the total airflow your air handler delivers (about 400 CFM per ton).
- 2Enter the conditioned floor area of the whole home.
- 3Enter the area of the room you are balancing.
Inputs explained
- System airflow(CFM)
- Enter the system airflow in CFM.
- Conditioned floor area(sq ft)
- Enter the conditioned floor area in sq ft.
- Room area(sq ft)
- Enter the room area in sq ft.
Worked example
Using the values the calculator loads with:
Inputs
- System airflow1200 CFM
- Conditioned floor area1800 sq ft
- Room area180 sq ft
Results
- Room supply airflow120 CFM
- CFM per sq ft0.67
- Share of system10%
- Suggested register count1
- 1,200 CFM x 180 / 1,800 = 120 CFM
Frequently asked questions
Is area-based splitting accurate?
It is a good first pass; a full Manual J load calculation adjusts for glazing, orientation and insulation.
How much CFM per register?
A typical residential supply register handles 100–150 CFM before it whistles.
What do I need to enter into the Room CFM Calculator?
Just 3 values: system airflow, conditioned floor area, room area. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Room CFM Calculator work out the answer?
Room airflow is normally allocated in proportion to floor area, at roughly 1 CFM per square foot for typical residential systems. It applies the formula room CFM = total CFM x room area / house area and shows the working so you can check each step by hand.
Is the Room CFM Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.