Fan operating point calculator

Enter airflow, pressure, power and fan geometry and get the full duty point in one place — air density, velocities, motor load and efficiency, static/total/impeller efficiency, torque, SFP, FEI (AMCA 208-18) and VDI 3731 sound power.

All-in-one duty point Motor load & FEI & acoustics Free, no sign-up

Fan data

Everything needed for the operating point — inputs only, all results are on the right.

Duty point

Airflow, pressure and power at the point you want to check.

Airflow

Unit

Pressure

Unit

Pressure is

Power at this point

Unit

This power is

Air conditions

Temperature °C

Altitude m

Sea-level pressure Pa

Relative humidity %

Motor

Nameplate rating — used for motor load and efficiency at this point.

Grid frequency

Rated power

Number of poles

IE efficiency class

Starting / drive type

Fan geometry & speed

Used for velocities, torque and the VDI 3731 sound estimate.

Duct / hydraulic diameter mm

Inlet diameter mm, optional

Rotor / impeller diameter mm

Number of blades

Fan construction (VDI 3731)

Rotor speed rpm

ErP 2026 compliance

Regulation (EU) 2024/1834 — its own classification, independent of the VDI 3731 fan construction above. Uses the airflow, pressure and power from the duty point.

Fan type

Blade type

Measurement category Annex III

VSD included in the assessment Dual use fan Reversible fan Low noise fan

Correction factors

Guard spacing e mm, blank if none

DC motor rated below 100 V AC/DC converter not part of the fan

Calculated operating point

Airflow: —
Static pressure: —
Total pressure: —
Dynamic pressure: —
Total pressure differential: —
Mass flow: —
Medium density: —
Linear velocity: —
Frequency: —
Rotational speed: —
Power consumption: —
Shaft power: —
Aerodynamic power: —
Shaft torque: —
Motor load ratio: —
Matched motor rating: —
Static efficiency: —
Total efficiency: —
Motor efficiency: —
Rotor (impeller) efficiency: —
Specific Fan Power: —
Fan Energy Index: —

ErP 2026 compliance

Compliance: —
Required minimum: —
Margin: —
N grade applied: —
Useful power P_u: —
Max. compliant power: —
Correction factors: —
Basis: —

VDI 3731 sound power

Sound power level: —

Link copied — it reopens with these exact inputs.

What this calculator does

A fan curve gives you airflow and pressure. Everything else an engineer actually needs — how loaded the motor is, whether the fan is running efficiently, whether it meets FEI, how loud it will be — takes several separate calculations. This tool runs them all from one duty point, reusing the exact same formulas as CloudAir's dedicated calculators:

Air density and atmospheric pressure, from temperature, altitude and humidity
Duct velocity and dynamic pressure, from airflow and hydraulic diameter
Motor load ratio and efficiency at that load, from IEC 60034-30-1 plus the induction-motor load/efficiency curve
Static, total and impeller (rotor) efficiency
Specific Fan Power and Fan Energy Index (AMCA 208-18)
ErP 2026 compliance against Regulation (EU) 2024/1834
VDI 3731 sound power level and octave-band spectrum, from fan construction and duty point

Electrical vs. shaft power

If the power you have is a wattmeter reading at the motor terminals, choose Electrical. If it comes off a fan curve — the manufacturer's shaft power at that airflow and pressure — choose Shaft, and the calculator derives the electrical draw from the motor's efficiency at that load.

This calculator combines IEC 60034-30-1 motor efficiency data, the AMCA 208-18 FEI reference-fan formula, Regulation (EU) 2024/1834 (ErP 2026) and the VDI 3731 Blatt 2 sound power method into a single duty point. The ErP fan family and blade type are inferred from the VDI 3731 construction choice above. It is provided for engineering guidance — always verify against the manufacturer's fan curve and datasheet before specifying equipment.