Enter any two of the four electrical values (voltage, current, resistance, power) and the calculator solves for the other two. All four formulas are shown.
Leave the fields you want to solve blank. At least two fields must be filled.
Ohm's law states that voltage equals current times resistance: V = I x R. Combined with the power formula P = V x I, you can solve for any unknown when two values are known.
A 12-volt DC circuit has a resistor of 6 ohms. What is the current and how much power does the resistor use?
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Ohm's law states that V = I x R. If you know any two of voltage, current, and resistance, you can solve for the third. Power adds a fourth variable: P = V x I. Enter any two values in this calculator and it solves for the remaining two automatically.
The three core rearrangements are: V = I x R (voltage equals current times resistance), I = V / R (current equals voltage divided by resistance), and R = V / I (resistance equals voltage divided by current). With power included, P = V x I is the fourth formula.
Using V = I x R: voltage = 20 x 12 = 240 volts. Power = V x I = 240 x 20 = 4,800 watts (4.8 kW).
Think of electricity like water in a pipe. Voltage is the water pressure, current is the flow rate, and resistance is how narrow the pipe is. Ohm's law says: the higher the pressure (voltage) or the wider the pipe (lower resistance), the more water flows (higher current). The formula is V = I x R.
Editor at Encore Editorial, Chris Terry sets the editorial standards here and turns dense topics into plain English. He has written widely on education, finance, and consumer markets.