Physics

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Ohm's Law Calculator.

Calculate voltage, current, resistance, and power

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Set your values

Results update as you type.

Results update automatically after you enter values.

How to Use

V = I × R · P = V × I

Enter any two of voltage, current, and resistance. Supplying all three checks their consistency.

Ideal DC relationship only; real circuits can include frequency, temperature, and component tolerances.

Cite this calculator

Canonical URL: https://mathify.one/fr/physics/ohms-law

Cite as: Mathify. (2026). Loi d'Ohm. https://mathify.one/fr/physics/ohms-law

Use Cases

Circuit Design and Troubleshooting

Quickly determine the required resistance or voltage for a given current in electronic circuits, or verify component values during troubleshooting.

Example: Find the resistance needed to limit current to 20 mA with a 9V supply.

Educational Learning and Homework

Check your answers for physics or electronics homework problems involving voltage, current, resistance, and power.

Example: Verify that a 12V battery with a 4Ω resistor produces 3A of current.

Frequently Asked Questions

What is Ohm's Law?
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance. It is expressed as V = I × R.
How do I use this calculator?
Enter any two known values among voltage, current, resistance, and power. The calculator will compute the remaining two using Ohm's Law and the power formula (P = V × I).
Can I calculate power with this calculator?
Yes, the calculator includes power calculation. If you provide voltage and current, it will compute power. Alternatively, you can enter resistance and current to find power.

Tips & Common Mistakes

Tips

  • Ensure you enter values in consistent units (volts, amps, ohms, watts) to get accurate results.
  • Use the calculator to cross-check your manual calculations for circuit problems.
  • Remember that Ohm's Law applies to linear resistive circuits; for non-linear components, results may vary.
  • If you know power and one other value, you can still find the missing parameters using the power formula.

Common Mistakes to Avoid

  • Mixing units, such as using milliamps with ohms without converting to amps.
  • Entering only one known value when two are required for calculation.
  • Assuming the calculator works for AC circuits with reactive components; it is designed for DC or purely resistive circuits.

Last updated: August 13, 2026