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 states that voltage equals current times resistance: V = I x R. Voltage is measured in volts (V), current in amperes (A), and resistance in ohms (Ω). If you know any two of the three, you can solve for the third by rearranging the equation.
How does the power triangle relate to Ohm's Law?
Power in a DC circuit is P = V x I. Substituting Ohm's Law gives two more forms: P = I^2 x R and P = V^2 / R. Together with V = I x R, these four equations let you derive any value from any two known quantities, which is exactly what this calculator does.
Does this calculator work for AC circuits?
Only for purely resistive AC loads when using RMS values. AC circuits with inductors or capacitors involve impedance, phase angle, and reactive versus real power, which this calculator does not model. For DC and resistive AC analysis it is exact.
How do I handle milliamps (mA) or milliohms (mΩ)?
Convert to base units first. 1 mA equals 0.001 A, and 1 mΩ equals 0.001 Ω. The calculator works in V, A, Ω, and W. So 250 mA at 5 V becomes 0.25 A and 5 V, which gives 20 Ω resistance and 1.25 W power.
What are some real circuit examples I can try?
A 12 V car bulb drawing 2 A has 6 Ω resistance and burns 24 W. A 5 V USB device pulling 0.5 A has 10 Ω resistance and uses 2.5 W. A 230 V kettle rated 2,000 W draws about 8.7 A through roughly 26 Ω of heating element. Drop any two known values in to verify.