Enter any two of voltage, current, resistance and power, and this calculator finds the other two using Ohm’s law and the power formula.
| Voltage (V) | – |
| Current (A) | – |
| Resistance (ohms) | – |
| Power (W) | – |
How it works
Ohm’s law says V = I × R: voltage equals current times resistance. Power is P = V × I. Combining them gives P = I² × R and P = V² ÷ R. With any two known values, the calculator picks the right formulas to find the other two.
This tool is for learning and simple checks. Work on mains electricity should be done by a qualified person.
Example
12 V across a circuit drawing 2 A means a resistance of 6 ohms and a power of 24 watts.
Frequently asked questions
What is Ohm’s law?
The relationship V = I × R between voltage, current and resistance.
How do I find power?
Multiply voltage by current. Power is measured in watts.
Does it work for AC?
It works for resistive loads. Reactive AC circuits need extra terms such as impedance and power factor.
More free tools: Electricity cost calculator · Unit converter · All free tools
For learning and simple checks only. Electrical work can be dangerous.