PWM Fan Speed Calculator
Estimated fan RPM and airflow from a PWM duty cycle.
Enter your values
Enter the full-speed rpm in rpm.
Enter the full-speed cfm in CFM.
Enter the pwm duty cycle in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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%
At a glance
| What it does | Estimated fan RPM and airflow from a PWM duty cycle. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Full-speed RPM, Full-speed CFM, PWM duty cycle |
| Main output | Estimated RPM |
| Formula | RPM = RPM_max x duty%; CFM = CFM_max x duty% |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Full-speed RPM(rpm)
- Enter the full-speed rpm in rpm.
- Full-speed CFM(CFM)
- Enter the full-speed cfm in CFM.
- PWM duty cycle(%)
- Enter the pwm duty cycle in %.
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.
What do I need to enter into the PWM Fan Speed Calculator?
Just 3 values: full-speed rpm, full-speed cfm, pwm duty cycle. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the PWM Fan Speed Calculator work out the answer?
PWM fan speed is approximately proportional to duty cycle once above the fan's minimum start-up duty cycle. It applies the formula RPM = RPM_max x duty%; CFM = CFM_max x duty% and shows the working so you can check each step by hand.
Is the PWM Fan Speed Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.