How Ohm's law works

Ohm's law relates voltage, current and resistance: V = I·R. Combined with the power law P = V·I, any two of the four quantities determine the other two — for example P = V²/R = I²·R. This calculator accepts any pair and solves the remaining values, formatting results with sensible units (µA/mA/A, Ω/kΩ/MΩ, mW/W).

Typical uses: finding the resistance that drops a given voltage at a given current, checking how much power a resistor must dissipate, or estimating the current a heater or LED strip draws from its power rating. Related tools: LED Resistor & Voltage Divider and the Resistor Color Code Calculator.