How to find Horsepower when ampere in known?

How to find Horsepower when ampere in known?
Horsepower = Engine Output Power.
Ampere = Input Current

Examples :
If given Ampere(I) = 5A ; Volt(V) = 240V ,
then, (I) x (V) = Watts(W),
is 5A x 240V = 1200W,
Next multiply watts by 0.00134 (1/746)and you will have horsepower.
1200W x 0.00134 = 1.608HP

So, basically the formula to get the horsepower are:
HP = (V) x (I) x (1/746),
More accurate is HP = [(V) x (I) x %eff x pf] x (1/746).

For 3 Phase Horsepower,
HP = [(V) x (I) x %eff x 1.73 x pf] x (1/746).

Where %eff = efficiency of the motor and pf = power factor..