Ohm's Law Calculator
Solve voltage, current or resistance from the other two — and get power in watts automatically.
Result
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Power —
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How it works
V = I × R; I = V ÷ R; R = V ÷ I; P = V × IFrequently Asked Questions
How does Ohm's law work?
Voltage equals current times resistance: a 12 V supply across a 6 Ω resistor drives 2 A of current, dissipating 24 W. Know any two of V, I, R and the third follows.
How do I calculate power from Ohm's law?
P = V × I, and by substitution P = I²R = V²/R. That is why halving resistance at fixed voltage doubles the current and doubles the power.
Why does wire gauge matter?
Thin wires have higher resistance, so at high current they drop voltage and heat up (P = I²R). Circuits are fused to keep current below what the wiring can safely dissipate.