Ohm's Law Calculator

Enter any two electrical values to instantly calculate voltage, current, resistance, or power. Free, fast, and easy to use.

Calculate

Choose what you want to find, enter your known values, and click Calculate Now to get instant results with step-by-step solutions.

Complete User Guide

What is Ohm's Law?

Ohm's law is a simple rule in electronics. It says that the voltage across a conductor is equal to the current flowing through it times the resistance. In short: V = I × R. This tool lets you find any missing value when you know the other two. It works for students, engineers, electricians, and hobbyists.

All Formulas at a Glance

Voltage: V = I × R

Current: I = V / R

Resistance: R = V / I

Power: P = V × I  |  P = I² × R  |  P = V² / R

4 Calculation Types

Voltage

Find voltage when you know current and resistance.

Current

Find current when you know voltage and resistance.

Resistance

Find resistance when you know voltage and current.

Power

Find power using three different formulas: V×I, I²×R, or V²/R.

How to Use This Calculator

  1. Pick what you want to find — voltage, current, resistance, or power.
  2. Enter the two values you already know.
  3. Choose units if needed (volts, millivolts, kilovolts, amps, milliamps, ohms, kilohms, etc.).
  4. Click Calculate Now and see your answer with a step-by-step breakdown and chart.

Quick Examples

• A 12V battery and 6Ω resistor: V / R = 12 / 6 = 2 A of current.

• A 5A current through 10Ω: I × R = 5 × 10 = 50 V.

• A 100W light bulb at 120V: P / V = 100 / 120 = 0.833 A.

Important Notes

  • All values must be positive numbers.
  • Resistance cannot be zero when used as a divisor.
  • Unit conversions are done automatically — just pick your preferred unit.
  • Ohm's law applies to resistive (linear) components. For reactive circuits, use impedance instead of resistance.

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