Fan Calculator

A fan transfers mechanical energy to moving air. The useful air power is the product of volumetric airflow and the pressure rise produced by the fan. In SI units, multiplying cubic metres per second by pascals gives watts directly. If a system needs 2 cubic metres per second at a 500 pascal rise, the air stream receives 1,000 watts. This relationship is a practical starting point for ventilation, extraction, cooling, and process-air estimates. Real fans do not convert all shaft power into useful air power. Total fan efficiency accounts for aerodynamic, mechanical, and other losses, so required shaft power equals air power divided by efficiency expressed as a decimal. At 80 percent efficiency, 1,000 watts of air power requires 1,250 watts at the shaft. Motor and drive losses may require still more electrical input. For electrical sizing, divide shaft power by motor and drive efficiencies as well and consider service factor and starting behavior. Pressure rise must represent the fan operating point, not an arbitrary catalog maximum. A duct system's resistance changes with airflow and includes straight-duct friction, filters, coils, dampers, fittings, terminals, and dynamic losses. The intersection of the fan curve and system curve determines actual flow and pressure. Density, temperature, altitude, inlet conditions, installation effects, and blade condition can shift performance away from a nominal rating. Use manufacturer curves for final equipment selection. This calculator assumes steady incompressible flow and uses one total efficiency value. It is well suited to preliminary comparisons and checks where airflow and pressure have already been established. It does not calculate duct pressure loss, noise, fan speed, impeller diameter, or a complete motor selection. Confirm whether a specification uses static or total pressure and pair it with the appropriate efficiency definition. A technically sound selection also checks the full duty range, motor loading, controllability, stall margin, acoustics, maintenance access, and applicable ventilation standards. Always allow for credible fouling and filter-loading conditions rather than sizing only at a clean-system point.