Enter any two known values and press "Calculate" to solve for the others. For example, a 100 watt light bulb operating on 120 volts AC will have 144 ohms of resistance and will draw 0.833 Amps. Enter 100 in the Watts field and 120 in the Voltage field and press Calculate to find the resistance and current. Fields should be reset to 0 before each new calculation.

Voltage (E) = Current (I) * Resistance (R)
Power (watts) = Current Squared (I^2) * Resistance (R)
Power = I*E = E^2 / R