Solve for Current: 12V, 100Ω Resistor

This page opens the Ohm's law calculator with a 12V supply and a 100Ω resistor already filled in — the result below is live, computed the moment the page loads, not a static example.

Solving for current is the most common Ohm's law question when you know the supply voltage and the resistor you are about to place in a circuit: I = V / R gives 12V / 100Ω = 0.12A, or 120mA. The calculator also derives power (P = VI), which here comes out to 1.44W — enough that a standard quarter-watt (0.25W) resistor would overheat, so this combination calls for at least a half-watt part.

Change either field above and the current, resistance, voltage and power all re-solve together — the tool works from any two known values, not just voltage and resistance, so it doubles as a check for whatever pair of numbers you actually have on hand.