Ohm's Law Calculator
Solve Ohm's law and the power formula. Enter any two values (voltage, current, resistance, or power) and the calculator finds the other two.
For learning and planning
Resistance (Ω)
6 Ω
Check the highlighted fields to see your result.
- Voltage (V)
- 12 V
- Current (A)
- 2 A
- Resistance (Ω)
- 6 Ω
- Power (W)
- 24 W
Results are estimates for information only and do not constitute financial, medical, or legal advice.
How it works
Ohm's law links voltage (V), current (I), and resistance (R). The power formula adds power (P). Since there are two equations and four values, knowing any two lets you work out the other two.
The formulas
V = I × R · P = V × I
I = V ÷ R · R = V ÷ I · P = I² × R = V² ÷ R
Worked example
A 12 V battery drives a current of 2 A through a lamp.
- Resistance: R = 12 ÷ 2 = 6 Ω.
- Power: P = 12 × 2 = 24 W.
Frequently asked questions
What does Ohm's law say?
The current through a conductor equals the voltage across it divided by its resistance: I = V ÷ R. Double the voltage and the current doubles; double the resistance and the current is cut in half.
How is power related to voltage and current?
Power in watts is voltage times current (P = V × I). Combined with Ohm's law, it can also be written as P = I² × R or P = V² ÷ R, which is why the calculator only needs two of the four values.
Does it work for AC circuits?
For resistive loads like heaters and incandescent bulbs, yes. Motors, transformers, and electronics add reactance and a power factor, so for them the simple formulas give only an approximation.