This calculator applies Ohm's law, the fundamental relationship between voltage, current and resistance in an electrical circuit. Enter current and resistance to find the voltage across a component.
What the symbols mean
- V — voltage (volts).
- I — current (amperes).
- R — resistance (ohms).
Worked example
A current of 2 A through a 10 Ω resistor produces a voltage of 2 × 10 = 20 V across it.
How the formula works
Ohm's law links the three core quantities of any circuit: voltage (the electrical push), current (the rate of charge flow) and resistance (the opposition to that flow). For a fixed voltage, higher resistance means less current. The relationship can be rearranged to find any one quantity from the other two.
Common mistakes to avoid
- Mixing up the variables. Keep clear which quantity you are solving for.
- Assuming all components are ohmic. Filament bulbs and diodes do not have constant resistance.
- Unit prefixes. Watch for milliamps and kilohms.
Where it is used
Ohm's law is the everyday workhorse of electronics: choosing resistors, sizing fuses, designing circuits, and diagnosing why a device draws too much current or runs hot.