Ohm’s law states that voltage across a linear resistor equals current times resistance: V = I × R.
Rearranged forms
- Current: I = V / R
- Resistance: R = V / I
Keep amperes in the formula. If your bench meter reads milliamps, divide by 1000 before you plug into the Ohm’s law calculator.
Where it applies
Ohm’s law is for the resistor itself, not the whole loop. A LED string still needs subtracting forward voltage before you solve for the ballast resistor. For AC reactance, magnitude-only sketches can treat |Z| like R, but capacitors and inductors need the reactance guide.