Fan Power Calculator (Shaft Power from Airflow and Pressure)
Power a fan or blower needs on its shaft from the airflow, the pressure it must add and its efficiency, together with the power that actually reaches the air.
Results
The dashed line marks the value you entered.
What this tool does
The useful power a fan puts into the air is simply the flow times the pressure rise, Q × Δp in watts when Q is in m³/s and Δp in pascals. The shaft has to supply more, by the fan's efficiency — commonly somewhere around 50–75 % — and the motor and drive draw a bit more again. Use matching quantities: static efficiency goes with static pressure, total efficiency with total pressure. Because power goes with the cube of speed in a given system, slowing a fan by a fifth cuts its power roughly in half.
Formula
air power = Q × Δp · shaft power = Q × Δp ÷ η (Q in m³/s, Δp in Pa)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
q | Flow rate | m³/h |
dp | Pressure the fan must add | Pa |
et | Efficiency | % |
PS | Shaft power needed | W |
PA | Power delivered to the air | W |
PK | Shaft power needed, in kilowatts | kW |
SP | Shaft power per cubic metre per second of air | kW/(m³/s) |
Worked example
- Flow rate5000 m³/h
- Pressure the fan must add500 Pa
- Efficiency65 %
- Shaft power needed1068 W
- Power delivered to the air694 W
- Shaft power needed, in kilowatts1.068 kW
- Shaft power per cubic metre per second of air0.77 kW/(m³/s)
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.