Hot Wire Anemometer CFM Calculator
CFM from averaged hot-wire velocity readings at low speed.
Enter your values
ⓘ Live results
Results
- Free area
- 1.5 sq ft
- Airflow
- 270 CFM
- Effective velocity (gross)
- 135 FPM
Quick answer
CFM equals the average hot-wire velocity reading multiplied by the measured free area of the opening.
CFM = V_avg x Free Area
How to use the Hot Wire Anemometer CFM Calculator
- 1Take multiple hot-wire readings across the grille or opening and average them.
- 2Enter the gross opening area and the grille's published free-area percentage.
- 3Multiply free area by average velocity to get CFM.
Worked example
Using the values the calculator loads with:
Inputs
- Average velocity reading180 FPM
- Gross opening area2.0 sq ft
- Free area ratio75 %
Results
- Free area1.5 sq ft
- Airflow270 CFM
- Effective velocity (gross)135 FPM
Frequently asked questions
Why free area, not gross area?
Hot-wire probes usually read velocity through the open portion of a grille, not the full frame area.
Hot wire vs vane anemometer?
Hot wire is more accurate at low velocities (below ~150 FPM) where vane anemometers lose accuracy.
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.