HP to Amps formulas are used to calculate current provided that HP (horsepower) is known in any circuit. Given below are the formulas:

HP to Amps Formula
In case of DC (HP x 746)/(E x %Efficiency)
Single phase AC (HP x 746)/(E x %Efficiency x PF)
Two phase four wire (HP x 746)/(E x %Efficiency x PF x 2)
Three phase (HP x 746)/(E x %Efficiency x PF x 1.73)

DC Circuit

Example: How much current a 0.5 HP DC motor having efficiency rating of 95% will draw at rated voltage of 12 volts.

Solution: I (DC) = (0.5 * 746) / (12 volts * 0.95)

I (DC) = 32.7


Single Phase AC Circuit

Example: A single phase 1/2 HP, 120 volt AC motor has efficiency rating of 90%. Find the current drawing by motor at power factor of 85%.

Solution: I (Single phase AC) = (0.5 * 746)/(120 * 0.9 * 0.85)

I (Single phase AC) = 4.06 Amps


Two phase four wire system

Example: Determine the current drawn by a two phase 1 HP, 230-volt motor having an efficiency rating of 90% and a power factor of 83%

Solution: I (Two phase AC) = (1 * 746)/(230 * 0.9 * 0.83 * 2)

I (Two phase) = 2.17 Amps


Three phase system

Example: A three phase, 1 HP, 230-volt motor having EF rating 85% operates at PF of 80%. Find the current drawn by the motor.

Solution: I (Three phase AC) = (1 * 746)/(230 * 0.85 * 0.8 * 1.73)

I (Three phase AC) = 2.75 Amps


So that was all about amps calculation from HP.

Let’s revise the formulas once: