How do you calculate hp to amps in 3 phase suply 415 volt?

One horsepower electric is 746 watts. Divide that by 415 to get amps, giving about 1.8. Divide that further by 3 because it is three phase power, giving about 0.6. Divide that further by power factor to compensate for apparent versus true power caused by reactance, say about 0.8, giving about 0.75.