HP to Amps Calculator

Horsepower describes a rate of mechanical work, while amperes describe electrical current. A motor's nameplate horsepower is mechanical output power, so current cannot be found from horsepower alone. The electrical supply must deliver additional power to cover motor losses, and alternating-current systems also require power factor. This calculator begins with the common conversion of one mechanical horsepower to 746 watts, then accounts for voltage, efficiency, supply type, and power factor. For a DC motor, estimated current equals output watts divided by voltage and decimal efficiency. For single-phase AC, the denominator also includes power factor. For balanced three-phase AC, it includes power factor and the square root of three. Efficiency must be entered as a percentage, such as 90 for a motor that converts 90 percent of electrical input into mechanical output. Power factor is a decimal between zero and one and represents how effectively apparent AC power becomes real power. The result is an engineering estimate of current at the entered operating point. Actual motor current varies with load, speed, design, temperature, supply quality, and manufacturer. Starting or locked-rotor current can be several times greater than normal full-load current, so this result must not be used as a direct substitute for conductor, disconnect, overload, or short-circuit protection requirements. Electrical codes often provide standardized full-load-current tables that intentionally differ from a calculation based on nominal efficiency and power factor. Use line-to-line voltage for a three-phase calculation and the operating supply voltage for DC or single-phase equipment. Obtain efficiency and power factor from the motor data sheet at the relevant load whenever possible. Small motors and lightly loaded motors may have substantially lower efficiency or power factor than assumed defaults. Also distinguish mechanical horsepower from electrical horsepower conventions and metric horsepower; this tool uses 746 watts per mechanical horsepower. This conversion is useful for early power-system estimates, comparing motors, checking whether a measured running current is plausible, and understanding the role of phase and losses. Final equipment selection should follow the motor nameplate, manufacturer instructions, applicable electrical code, service factor, duty cycle, ambient conditions, and a qualified electrical design.