Ohm's Law Calculator
Voltage, current, power.
Enter the values and press Calculate.
How to use Ohm's Law Calculator
Ohm's law links voltage, current, and resistance; power follows from voltage and current.
Open Ohm's Law Calculator on toolpermarket and enter your values above.
Enter a voltage and a resistance in the fields above, then press Calculate.
Read the result below the form. You can change any input and press Calculate again to compare scenarios.
Worked example. 12 volts across 4 ohms draws 3 amps and uses 36 watts.
When to use Ohm's Law Calculator. Use it for basic circuit design and electronics troubleshooting.
When you actually reach for this
- Use it for basic circuit design and electronics troubleshooting.
Where this tool stops being accurate
- Assumes ideal conditions - no friction, constant g, ideal gas - and consistent SI units; mixing units gives a wrong answer.
- Real measurements carry error, and the model ignores secondary effects.
Frequently asked questions
What if resistance is zero?
That would be a short circuit with infinite current, so the tool requires positive resistance.
Can I find voltage instead?
This version takes voltage and resistance; swap inputs to compute the other way around.
Why did I get the wrong unit?
Almost always a unit mismatch. Keep everything in one system (SI) before calculating, or convert first; the formula itself is exact.