Fan CFM from RPM Calculator
Apply fan law one to a speed change.
Enter your values
ⓘ Live results
Results
- New airflow
- 1,250 CFM
- New static pressure
- 0.781 in wc
- New power
- 0.977 HP
- Speed ratio
- 1.25
- Power change
- 95.3%
Quick answer
Airflow scales directly with fan speed, pressure with the square of speed and power with the cube.
CFM2 = CFM1 x (RPM2 / RPM1)
How to use the Fan CFM from RPM Calculator
- 1Enter the airflow, static pressure and power at the current speed.
- 2Enter the new RPM you plan to run.
- 3Check the motor can handle the cubed power increase before speeding a fan up.
Worked example
Using the values the calculator loads with:
Inputs
- Current airflow1000 CFM
- Current speed800 RPM
- New speed1000 RPM
- Current static0.5 in wc
- Current power0.5 HP
Results
- New airflow1,250 CFM
- New static pressure0.781 in wc
- New power0.977 HP
- Speed ratio1.25
- Power change95.3%
Frequently asked questions
Why does slowing down save so much?
Power follows the cube of speed — a 20% speed cut halves the power draw.
Do the laws always hold?
They assume the same fan, air density and system curve; big density changes need correction.
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.