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.
A 12-volt DC circuit has a resistor of 6 ohms. What is the current, and how much power does the resistor use? Two values are enough to answer both questions.
| Solve for | Formula |
|---|---|
| Voltage | V = I x R |
| Current | I = V / R |
| Resistance | R = V / I |
| Power (from V, I) | P = V x I |
| Power (from I, R) | P = I^2 x R |
| Power (from V, R) | P = V^2 / R |
Ohm's law states that voltage equals current times resistance: V = I x R. Combined with the power formula P = V x I, any two known values are enough to solve for the other two, since the calculator above substitutes one formula into the other rather than needing a fourth measurement.
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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.
Marcus Vance spent a decade building data pipelines and testing calculation logic before he started writing about the math behind the tools. On MathCalcTools he checks every formula against the source math, then writes out the steps so a reader can follow the same path a calculator takes.