Electronics
Power from Ohm's law
Three equivalent forms. Use whichever matches the two quantities you already hold.
The Formula
P = V x I = I^2 x R = V^2 / R
Three equivalent forms. Use whichever matches the two quantities you already hold.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| P | Power dissipated by the component | watts | For 12 volts and 2 amperes this is 24 watts by every one of the three forms. |
| V | Voltage across the component | volts | Appears squared in the form P = V^2 / R. |
| I | Current through the component | amperes | Appears squared in the form P = I^2 x R, which is why doubling current quadruples power. |
What Each Symbol Means
Pwatts
Power dissipated by the component
For 12 volts and 2 amperes this is 24 watts by every one of the three forms.
Vvolts
Voltage across the component
Appears squared in the form P = V^2 / R.
Iamperes
Current through the component
Appears squared in the form P = I^2 x R, which is why doubling current quadruples power.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate ohm's law 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 Ohm's Law, filed under Science. Every number the guide produces comes from substituting into this one line.