Formula:
1 Ph.Amps = ((( (746 / hp) / V ) / E.F ) / P.F )
1.FLA = ( (1 Ph.Amps) x 1.25 )
3 Ph.Amps = (((( (746 / hp) / 1.732 ) / V ) / E.F ) / P.F )
3.FLA = ( (3 Ph.Amps) x 1.25 )
where,
V - Volts,
E.F - Efficiency,
P.F - Power factor,
FLA - Full Load Amps.
Calculation of Electric motor hp to amps is made easier here.