Ohm's Law Calculator
Fill in any two of the four values and leave the other two blank. The calculator solves for the missing quantities using V = I × R and P = V × I.
Result
- Voltage
- 12 V
- Current
- 2 A
Formula
- V = I × R
- I = V ÷ R
- R = V ÷ I
- P = V × I = I² × R = V² ÷ R
How the Ohm's Law Calculator works
Ohm's law says the voltage across a resistor equals the current through it times its resistance. Combined with the power formula P = V × I, any two of the four quantities fix the other two.
The law applies to resistive DC circuits and to the resistive part of AC circuits. Components such as diodes and LEDs do not follow it, because their resistance changes with voltage.
Worked example
A 12 V supply driving 2 A: R = 12 ÷ 2 = 6 Ω, and P = 12 × 2 = 24 W.
Frequently asked questions
What is Ohm's law in simple terms?
Voltage equals current times resistance. Doubling the voltage across a fixed resistor doubles the current. Doubling the resistance at a fixed voltage halves the current.
How do I calculate current from watts and volts?
Divide power by voltage. A 60 W lamp on 120 V draws 60 ÷ 120 = 0.5 A.
How do I find resistance from power and voltage?
Square the voltage and divide by the power. A 1,500 W heater on 120 V has a resistance of 120² ÷ 1,500 = 9.6 Ω.
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