⚡ Ohm's Law
Voltage, current, resistance and power
About this calculator
Ohm's Law is the foundation of all electrical work: voltage equals current times resistance (V = I × R). Give this calculator any two of the three values — voltage in volts, current in amps, resistance in ohms — and it solves for the missing one, plus electrical power (P = V × I). Electricians use it to size breakers and wire; hobbyists use it to pick resistors for LED circuits so they don't burn out.
The math is simple division or multiplication, but the units trip people up: 1,000 milliamps = 1 amp, and power in watts tells you the heat a component must handle. Practical tip: when in doubt, choose a resistor with at least double the calculated wattage rating — running components at their limit is how the magic smoke escapes.