Ohm's Law Calculator
Enter any two of voltage, current and resistance to get the third and the power. V = I × R, P = V × I.
What is Ohm's law?
The voltage across a conductor equals the current through it multiplied by its resistance: V = I × R. Knowing any two of the three quantities gives you the third.
- Voltage (V), in volts: the push behind the electricity.
- Current (I), in amperes: how much charge flows.
- Resistance (R), in ohms: how strongly the conductor opposes the flow.
How is power calculated?
The power dissipated in a resistor is P = V × I. The same result comes from I² × R or V² / R.
Example
If 2 amperes flow through a 12 ohm resistor, the voltage across it is 2 × 12 = 24 volts and the power is 24 × 2 = 48 watts.
Where does it not apply?
Ohm's law applies directly to direct current and to purely resistive loads such as heaters and incandescent lamps. For inductive loads such as motors and transformers on alternating current, impedance replaces resistance and the power factor (cos φ) enters the power formula.
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