Fan RPM Change Calculator
Required RPM to hit a target CFM.
Enter your values
ⓘ Live results
Results
- Required RPM
- 1,160 rpm
- RPM change
- 160 rpm
- Speed ratio
- 1.16
- Expected pressure ratio
- 1.346
- Expected power ratio
- 1.561
Quick answer
Required RPM is the current RPM multiplied by the ratio of target CFM to current CFM.
N2 = N1 x (CFM2/CFM1)
How to use the Fan RPM Change Calculator
- 1Enter your current CFM and RPM from a field measurement or fan curve.
- 2Enter the target CFM you need.
- 3Read the RPM to dial in on the drive or VFD, plus the expected pressure and power change.
Worked example
Using the values the calculator loads with:
Inputs
- Current CFM5000 CFM
- Current RPM1000 rpm
- Target CFM5800 CFM
Results
- Required RPM1,160 rpm
- RPM change160 rpm
- Speed ratio1.16
- Expected pressure ratio1.346
- Expected power ratio1.561
Frequently asked questions
Can I just set the VFD to this frequency?
Yes if driven by a VFD at fixed motor poles — RPM is proportional to frequency.
What if I have a belt drive?
Use this RPM as the target fan shaft speed, then resize the sheaves accordingly.
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.