Specific Fan Power Calculator
SFP in W/(L/s) or W/CFM for system efficiency comparison.
Enter your values
Enter the total fan power in W.
Enter the design airflow in CFM.
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.
- Specific fan power
- 1.554 W/(L/s)
- Specific fan power
- 0.733 W/CFM
- Airflow in L/s
- 1,416 L/s
- Rating
- Good
Quick answer
Specific fan power is total fan power divided by design airflow, commonly expressed in watts per litre-per-second.
SFP = Power(W) / Airflow(L/s)
At a glance
| What it does | SFP in W/(L/s) or W/CFM for system efficiency comparison. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Total fan power, Design airflow |
| Main output | Specific fan power |
| Formula | SFP = Power(W) / Airflow(L/s) |
| Cost | Free — no sign-up, no download |
How to use the Specific Fan Power Calculator
- 1Enter the total electrical power of the fan(s) serving the airflow, including all fans in the air path.
- 2Enter the design airflow.
- 3Compare the resulting SFP against your code or green-building target (many targets are under 1.5-2.0 W/(L/s)).
Inputs explained
- Total fan power(W)
- Enter the total fan power in W.
- Design airflow(CFM)
- Enter the design airflow in CFM.
Worked example
Using the values the calculator loads with:
Inputs
- Total fan power2200 W
- Design airflow3000 CFM
Results
- Specific fan power1.554 W/(L/s)
- Specific fan power0.733 W/CFM
- Airflow in L/s1,416 L/s
- RatingGood
Frequently asked questions
Why W/(L/s) and not W/CFM?
W/(L/s) is the standard metric in European and many green-building codes; W/CFM is more common in the US.
What counts as 'total fan power'?
Include supply, return, exhaust fans and any series fans in that airflow path per your code's definition.
What do I need to enter into the Specific Fan Power Calculator?
Just 2 values: total fan power, design airflow. 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 Specific Fan Power Calculator work out the answer?
Specific fan power is total fan power divided by design airflow, commonly expressed in watts per litre-per-second. It applies the formula SFP = Power(W) / Airflow(L/s) and shows the working so you can check each step by hand.
Is the Specific Fan Power 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.