According to the law of conservation of energy, the total energy of a system remains constant, though energy may transform into another form. Two billiard balls colliding, for example, may come to rest, with the resulting energy becoming sound and perhaps a bit of heat at the point of collision.
The SI unit of energy is the joule (J) or newtonmeter (N * m). The joule is also the SI unit of work.
Energy converter  

P = IE
P = Power (Watts)
I = Current (Amps)
E = Voltage (Volts)
So: I= P/E
E = P/I
1 Watt = 1 Ampere * 1 Volt
Example:
Convert the energy for the given details. For given attojoule into calorie.
Convert value = 5 attojoule
Convert to = Calorie (I.T.)
Solution:
Calorie (I.T.) = 1.1942294831374797e18