Enter any two known values to solve for voltage, current, resistance, and power.
Choose which two quantities you already know, enter their values, and the calculator solves for the remaining two using Ohm's Law and the power formula. All four electrical quantities — voltage, current, resistance, and power — are shown together once calculated, so you can see the full picture of the circuit.
Ohm's Law states that voltage equals current multiplied by resistance: V = I × R. This relationship can be rearranged to solve for any one of the three quantities given the other two: I = V / R, or R = V / I.
Electrical power is calculated as P = V × I, the product of voltage and current. Combined with Ohm's Law, power can also be expressed purely in terms of current and resistance (P = I²R) or purely in terms of voltage and resistance (P = V²/R), which is how this calculator solves for power when only resistance and one other value are known.
Voltage is in volts (V), current is in amperes/amps (A), resistance is in ohms (Ω), and power is in watts (W) — the standard SI units for each quantity in basic circuit analysis.
Using P = V²/R, power can be calculated directly from voltage and resistance without needing current as an intermediate step. The calculator handles this automatically once it derives current from your two known values.
This calculator applies to simple DC (direct current) circuits or to the resistive (real) portion of AC circuits. AC circuits with reactive components like capacitors and inductors involve impedance and phase angles, which require a more complete AC circuit analysis beyond basic Ohm's Law.