The Ohm's Law Calculator finds voltage, current, resistance or power from any two of them.
| Voltage (V) | 110 V |
| Current (I) | 0.2 A |
| Resistance (R) | 550 Ω |
| Power (P) | 22 W |
Ohm's law, discovered by Georg Ohm in 1827, states that the current through a conductor is proportional to the voltage across it: V = I × R. Combined with the power law P = V × I, any two of voltage, current, resistance and power determine the other two.
V = I × R. I = V ÷ R. R = V ÷ I. P = V × I = I²R = V²/R.
Worked example (defaults): 110 V and 0.2 A give R = 550 Ω and P = 22 W.
Voltage in volts (V), current in amperes (A), resistance in ohms (Ω), power in watts (W). Prefixes: milli (m) = 1/1000, kilo (k) = 1,000, mega (M) = 1,000,000.
Choose resistors and wires rated for the power and current they carry, with a safety margin. Ohm's law applies to resistive loads; motors, LEDs and other non-linear devices behave differently.
Why does a wire get hot? Power I²R is turned into heat.
What is impedance? Resistance's AC counterpart, including reactance.
Is high voltage dangerous? Current through the body is what harms, but higher voltage drives more current.