Room CFM Calculator
Supply CFM a room needs from its square footage.
Enter your values
ⓘ Live results
Results
- 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
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.
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.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.