Physics
Power from energy and time
Divide the energy by the interval to get the rate. With joules and seconds the result is already in watts.
The Formula
P = W / t
Divide the energy by the interval to get the rate. With joules and seconds the result is already in watts.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| W | Work or energy transferred | joules | In joules. The quantity that moves, not the speed at which it moves. |
| t | Time taken | seconds | In seconds. Using hours here breaks the result, because a watt is a joule per second. |
| P | Power | watts | The rate of energy transfer. 3600 J over 12 s gives 300 W. |
What Each Symbol Means
Wjoules
Work or energy transferred
In joules. The quantity that moves, not the speed at which it moves.
tseconds
Time taken
In seconds. Using hours here breaks the result, because a watt is a joule per second.
Pwatts
Power
The rate of energy transfer. 3600 J over 12 s gives 300 W.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate power page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Power, filed under Science. Every number the guide produces comes from substituting into this one line.