Squirrel Cage Fan CFM Calculator
Estimate CFM output of a squirrel-cage (forward-curved) blower.
Enter your values
Enter the wheel diameter in in.
Enter the wheel width in in.
Enter the wheel rpm in rpm.
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 free-air CFM
- 15 CFM
- Tip speed
- 2880 FPM
- Note
- Free-air estimate; ducted CFM will be lower against system resistance
Quick answer
A forward-curved squirrel-cage blower's free-air CFM can be approximated from its wheel diameter, width and tip speed.
CFM ~ k x D^2 x W x RPM (empirical forward-curved blower approximation)
At a glance
| What it does | Estimate CFM output of a squirrel-cage (forward-curved) blower. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Wheel diameter, Wheel width, Wheel RPM |
| Main output | Estimated free-air CFM |
| Formula | CFM ~ k x D^2 x W x RPM (empirical forward-curved blower approximation) |
| Cost | Free — no sign-up, no download |
How to use the Squirrel Cage Fan CFM Calculator
- 1Enter the squirrel-cage wheel's diameter, width and RPM.
- 2The tool applies a typical empirical constant for forward-curved blowers to estimate free-air CFM.
- 3Confirm against the manufacturer's fan curve at your actual static pressure, since this is a free-air estimate only.
Inputs explained
- Wheel diameter(in)
- Enter the wheel diameter in in.
- Wheel width(in)
- Enter the wheel width in in.
- Wheel RPM(rpm)
- Enter the wheel rpm in rpm.
Worked example
Using the values the calculator loads with:
Inputs
- Wheel diameter10 in
- Wheel width8 in
- Wheel RPM1100 rpm
Results
- Estimated free-air CFM15 CFM
- Tip speed2880 FPM
- NoteFree-air estimate; ducted CFM will be lower against system resistance
Frequently asked questions
Why is this only an estimate?
Actual CFM depends heavily on blade geometry and housing (scroll) design, which vary by manufacturer.
Forward-curved vs backward-curved?
Forward-curved (squirrel cage) wheels give more CFM for a given size at low pressure and low RPM but are less efficient than backward-curved wheels.
What do I need to enter into the Squirrel Cage Fan CFM Calculator?
Just 3 values: wheel diameter, wheel width, wheel rpm. 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 Squirrel Cage Fan CFM Calculator work out the answer?
A forward-curved squirrel-cage blower's free-air CFM can be approximated from its wheel diameter, width and tip speed. It applies the formula CFM ~ k x D^2 x W x RPM (empirical forward-curved blower approximation) and shows the working so you can check each step by hand.
Is the Squirrel Cage Fan CFM 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.