How to convert electric power in watts (W) to energy in joules (J).
You can calculate joules from watts and seconds, but you can't convert watts to joules since watt and joule units represent different quantities.
Watts to joules calculation formula
The energy E in joules (J) is equal to the power P in watts (W), times the time period t in seconds (s):
E(J) = P(W) × t(s)
So
joules = watts × seconds
or
J = W × s
Example
What is the energy consumption of an electrical circuit that has power consumption of 30 watts for time duration of 3 seconds?
E(J) = 30W × 3s = 90J