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Fan Airflow, Pressure Rise and DC Input Power

Balance fan air power, volumetric flow per minute and pressure rise with DC voltage, current and overall efficiency; solve any unknown using selectable units.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

A 100 V DC supply delivering 2 A uses 200 W. At 50% overall efficiency, 100 W of air power across a 100 Pa pressure rise corresponds to 1 m³/s: 60 m³/min or about 2,118.88 CFM.

P_in = VI; P_air = ηP_in = Δp Q (Q in m³/s); Q_CFM = 60 P_air/(0.3048³ Δp).

Worked example

Enter these known values and leave the other values blank.

DC voltage V
100 V
DC current I
2 A
Overall efficiency η (fraction)
0.5
Pressure rise Δp
100 Pa
Air power P_air
100 W
Volumetric airflow Q
2119 cu ft / min
DC electrical input P_in
200 W

Assumptions and limitations

  • This is a steady, low-Mach pressure-work balance at a supplied operating point. It uses approximately incompressible volume flow and positive pressure rise; it does not find a fan curve, system operating point, speed or affinity-law scaling.
  • Pressure is a rise Δp across the fan, not absolute atmospheric pressure. Static or total pressure and the efficiency definition must use a matching basis. Q is volumetric flow, not mass flow; the captured fixed minute denominator is preserved for every volume choice.
  • Electrical input VI is DC real power or a DC-equivalent input. AC voltage and current alone do not determine real input power: power factor, phase and motor/control losses require their own model. A known real electrical input can be entered directly.
  • η is overall electrical-input-to-air-power efficiency, entered as a fraction: 0.5 means 50%. The editable locked default 1 is an ideal limit. Motor-only efficiency is not automatically the fan-system overall efficiency.
  • The retained model requires positive air power, electrical power, voltage, current, pressure rise and flow, with 0 < η ≤ 1. Zero-flow/off-state and reverse-flow modes are outside this captured positive model. Clear and unlock an unknown to solve its inverse.
  • Mechanical hp and air hp use 550 ft·lbf/s; metric hp uses 75 kgf·m/s and electric hp is 746 W. US liquid gallons and imperial gallons differ. Mercury-pressure units retain their stated conventional conversion; Torr is exactly 1/760 atmosphere.

Common questions

Does this predict the actual airflow of my fan?

It gives the flow consistent with the supplied pressure rise and air power under a steady pressure-work model. Actual airflow also depends on a fan curve and system resistance, which this tool does not solve.

Can I enter AC mains voltage and current?

VI here represents DC real input power. AC real power also depends on phase and power factor; first determine real input power with the appropriate electrical model.

Is CFM a mass flow rate?

No. CFM is cubic feet per minute, a volume flow rate. A mass flow needs air density as well.

References

The captured input-power validation repeats the output-power variable. Add a source-pinned positive electrical input condition while retaining the original positive-flow operating model and 0 < overall efficiency ≤ 1. For steady pressure-work flow, P_air=Δp Q with Q in m³/s. The exact international-foot CFM conversion is 60/(0.3048³), replacing the captured rounded 2122.7878 factor. All first-equation inverses use the same exact relation. Six division guards retain finite positive behavior while leaving singular or invalid inverses blank. VI remains DC real electrical input and η is overall input-to-air efficiency. Mechanical horsepower uses exactly 550 foot-pounds-force per second instead of a rounded factor. Pounds-force per square inch use the exact international pound and inch with standard gravity, replacing the rounded captured factor. Mercury pressure columns use conventional density and standard gravity, with the exact international inch. Pounds-force per square foot use the exact international pound and foot with standard gravity. Bookify replaces the captured rounded US gallon with the exact 3.785411784-liter definition.

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