Tech
Ohm's Law Calculator
Solve voltage, current, resistance, and power from any two known values. Uses V = I x R and the DC power equations with full formula trace.
Solve for the missing values
Enter any two of the four values. The calculator solves for the other two using Ohm's Law and the DC power equations.
V
A
Ω
W
Provided: 2 of 2 needed
Voltage
12 V
Current
0.5 A
Resistance
24 Ω
Power
6 W
Formulas used
- R = V / I
- P = V * I
Frequently Asked Questions about the Ohm's Law Calculator
What is Ohm's Law and the V = I x R formula?
Ohm's Law says voltage equals current times resistance: V = I x R. Voltage is in volts (V), current in amperes (A), and resistance in ohms. Rearrange to find any one of the three when you know the other two: I = V / R or R = V / I. This calculator also includes power, so you only need any two of the four quantities to get all four results.
How does the power triangle relate to Ohm's Law?
DC power is P = V x I. Substitute Ohm's Law into that and you get two more forms: P = I^2 x R and P = V^2 / R. Combined with V = I x R, these four equations let you derive any unknown from any two knowns. Enter any two values and the calculator solves the other two using exactly those formulas.
Does this calculator work for AC circuits?
It works correctly for resistive AC loads when you use RMS values for voltage and current. For circuits with inductors or capacitors, the opposition to current is impedance, not pure resistance, and real power differs from apparent power. The calculator does not model reactance, phase angle, or power factor, so it is not suitable for inductive or capacitive AC analysis.
How do I handle milliamps (mA) or milliohms (mOhm)?
Convert to base units before entering values. 1 mA = 0.001 A, and 1 milliohm = 0.001 ohms. For example, a circuit at 5 V drawing 250 mA: enter 5 for voltage and 0.25 for current. The calculator returns 20 ohms resistance and 1.25 W power. The same applies to kilohms (1 kohm = 1000 ohms) or microamps.
What are some real circuit examples I can try?
A 12 V car bulb drawing 2 A has 6 ohms resistance and dissipates 24 W. A 5 V USB device pulling 500 mA (0.5 A) has 10 ohms resistance and uses 2.5 W. A 120 V US household circuit protected by a 15 A breaker can deliver up to 1,800 W through 8 ohms of load. Enter any two values to verify the others.