Power is simply the amount of energy used or the amount of "work" a circuit is doing.
Power is represented by the letter P. The basic unit for measuring power is watts or the letter W. To find power, all you need is a simple equation:
or Power equals voltage times current.
For example, if
E = 9V
I = 0.5A
P = 9 * 0.5
P = 4.5W