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Calculation Machine

Specific Fan Power Calculator

SFP in W/(L/s) or W/CFM for system efficiency comparison.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
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.

The formula

SFP = Power(W) / Airflow(L/s)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Total fan power2200 W
  • Design airflow3000 CFM

Result

  • Specific fan power1.554 W/(L/s)
  • Specific fan power0.733 W/CFM
  • Airflow in L/s1,416 L/s
  • RatingGood

How to use the Specific Fan Power Calculator

  1. 1Enter the total electrical power of the fan(s) serving the airflow, including all fans in the air path.
  2. 2Enter the design airflow.
  3. 3Compare the resulting SFP against your code or green-building target (many targets are under 1.5-2.0 W/(L/s)).

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.

About this calculator