How it's calculated
P = V × I = V² ÷ R = I² × R
P = power (watts), V = voltage (volts), I = current (amps), R = resistance (ohms). Enter any two of V, I, R; based on Ohm's law and the DC power equation.
Common questions
How do I calculate watts from volts and amps?
Multiply them: watts = volts × amps. A 120 V circuit drawing 5 A uses 600 watts.
How do I find watts from current and resistance?
Use P = I² × R. A 2 A current through 10 ohms dissipates 40 watts.