PWM Fan Speed Calculator
Estimated fan RPM and airflow from a PWM duty cycle.
Enter your values
ⓘ Live results
Results
- Estimated RPM
- 1,000 rpm
- Estimated airflow
- 30 CFM
- Estimated noise reduction
- 88% less power vs full speed
Quick answer
PWM fan speed is approximately proportional to duty cycle once above the fan's minimum start-up duty cycle.
RPM = RPM_max x duty%; CFM = CFM_max x duty%
How to use the PWM Fan Speed Calculator
- 1Enter the fan's full-speed RPM and CFM rating.
- 2Enter the PWM duty cycle percentage from the controller.
- 3Read the estimated RPM and airflow — actual response is roughly linear but flattens near minimum duty.
Worked example
Using the values the calculator loads with:
Inputs
- Full-speed RPM2000 rpm
- Full-speed CFM60 CFM
- PWM duty cycle50 %
Results
- Estimated RPM1,000 rpm
- Estimated airflow30 CFM
- Estimated noise reduction88% less power vs full speed
Frequently asked questions
Why not exactly linear at low duty?
Most PWM fans have a minimum duty cycle (often 20-30%) below which they stall or run at a fixed minimum speed.
Does this apply to computer case fans?
Yes, this approximation is commonly used for PC and server PWM fans.
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.