The most important equation in electronics
Ohm's law ties together the three fundamental quantities of an electrical circuit: voltage, current, and resistance. Master it and you can analyse or design almost any simple circuit, size a resistor, or diagnose why a component is running hot. This calculator solves the relationship for whichever value you do not know, and also gives you the power.
How to use the calculator
Enter any two of voltage (volts), current (amps), and resistance (ohms), leaving the third blank. The calculator finds the missing quantity and also reports the power dissipated in watts.
The formula and a helpful analogy
V = I × R. A water-pipe analogy makes it intuitive: voltage is the water pressure, current is the rate of flow, and resistance is how narrow the pipe is. More pressure pushes more water through; a narrower pipe restricts it. Rearranged, current = voltage ÷ resistance and resistance = voltage ÷ current.
Power and why thin wires get hot
Electrical power is voltage times current, P = V × I, measured in watts — a 60 W bulb on a 240 V supply draws 0.25 A. Power can also be written P = I²R, which explains why undersized wires overheat: for a given current, higher resistance produces more heat. That is the principle behind everything from a toaster element to a blown fuse, and why choosing the right cable thickness matters for safety.