Fan Laws Calculator
Calculate how airflow, pressure, and power change with fan speed, per the fan laws.
Result
Speed
1,500
Airflow
3,000
Pressure
2.25
Power
1.688
Usage examples
Predicting airflow after changing fan speed with a VFD
If you know the current speed and airflow, see exactly how airflow changes when you adjust speed with a variable frequency drive.
Estimating speed and power needed for a target airflow
Set your desired airflow first, and back-calculate the speed ratio and resulting power change needed to reach it.
Seeing how speed changes affect power draw
Since power scales with the cube of speed, see how much even a small speed change affects power consumption.
Frequently asked questions
What are the fan laws?
For the same fan system, when speed changes, airflow scales linearly with speed, pressure scales with the square of speed, and power scales with the cube of speed.
Can I calculate without knowing pressure or power?
Yes. Pressure and power are optional — leave them blank and only airflow and speed will be calculated.
Does this hold true in every situation?
The fan laws assume the system resistance characteristic (like the ductwork) doesn't change. If duct or damper conditions change, actual values will differ.
Should I solve by target RPM or target airflow?
Use target RPM if you're targeting a specific speed (like a VFD setpoint), or target airflow if you're targeting a specific CFM.