Fan Inlet Velocity Calculator
Air velocity entering a fan's inlet cone or box.
Enter your values
Enter the fan airflow in CFM.
Enter the inlet diameter in 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.
- Inlet velocity
- 4,584 FPM
- Inlet area
- 2.182 sq ft
- Rating
- High - check for noise and efficiency loss
Quick answer
Fan inlet velocity equals CFM divided by the inlet's free area.
V = CFM / Area
At a glance
| What it does | Air velocity entering a fan's inlet cone or box. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Fan airflow, Inlet diameter |
| Main output | Inlet velocity |
| Formula | V = CFM / Area |
| Cost | Free — no sign-up, no download |
How to use the Fan Inlet Velocity Calculator
- 1Enter the fan's design CFM and the diameter of the inlet cone or duct connection.
- 2Read the resulting inlet velocity.
- 3Keep inlet velocity moderate (often under ~2,500-3,000 FPM) to minimize noise and turbulence losses.
Inputs explained
- Fan airflow(CFM)
- Enter the fan airflow in CFM.
- Inlet diameter(in)
- Enter the inlet diameter in in.
Worked example
Using the values the calculator loads with:
Inputs
- Fan airflow10000 CFM
- Inlet diameter20 in
Results
- Inlet velocity4,584 FPM
- Inlet area2.182 sq ft
- RatingHigh - check for noise and efficiency loss
Frequently asked questions
Why does high inlet velocity hurt performance?
Turbulent, uneven inlet flow (system effect) reduces the fan's effective pressure and increases noise, sometimes significantly.
What about outlet velocity?
Outlet (discharge) velocity should also be checked separately against duct connection guidelines.
What do I need to enter into the Fan Inlet Velocity Calculator?
Just 2 values: fan airflow, inlet diameter. 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 Fan Inlet Velocity Calculator work out the answer?
Fan inlet velocity equals CFM divided by the inlet's free area. It applies the formula V = CFM / Area and shows the working so you can check each step by hand.
Is the Fan Inlet Velocity 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.