Velocity Pressure to FPM Calculator
Convert pitot velocity pressure to air speed.
Enter your values
ⓘ Live results
Results
- Air velocity
- 896 FPM
- In m/s
- 4.55
- Airflow
- 488 CFM
- Duct area
- 0.545 sq ft
Working
- 14005 x sqrt(0.05) = 896 FPM
Quick answer
Air velocity equals 4,005 times the square root of velocity pressure in inches of water at standard air density.
FPM = 4005 x sqrt(Vp)
How to use the Velocity Pressure to FPM Calculator
- 1Take the velocity pressure reading with a pitot tube and manometer.
- 2Average a proper traverse of readings across the duct.
- 3Multiply the average velocity by the duct area for airflow.
Worked example
Using the values the calculator loads with:
Inputs
- Velocity pressure0.05 in wc
- Duct diameter10 in
Results
- Air velocity896 FPM
- In m/s4.55
- Airflow488 CFM
- Duct area0.545 sq ft
- 4005 x sqrt(0.05) = 896 FPM
Frequently asked questions
Where does 4005 come from?
It bundles standard air density of 0.075 lb/ft³; correct it for hot or high-altitude air.
Total, static and velocity pressure?
Total equals static plus velocity; a pitot tube measures the difference to give velocity pressure directly.
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.