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Ohm’s Law Calculator

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Ohm’s Law defines the fundamental relationship between voltage (V), current (I), and resistance (R) in any electrical circuit. This is the most important formula in all of electronics. Enter any two known values below and the calculator will instantly compute the third using the correct Ohm’s Law formula.

V = I × R · I = V ÷ R · R = V ÷ I · P = V × I
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How to use this calculator

Step-by-Step Instructions

1. **Identify your known values** Determine which two electrical values you already know from your circuit: Voltage (in Volts), Current (in Amps), or Resistance (in Ohms).
2. **Enter the two known values** Type them into the corresponding input fields. Leave the unknown field completely empty.
3. **Click “Calculate”** The calculator automatically selects the correct formula (V=IR, I=V/R, or R=V/I) and computes the missing value.
4. **Read your result** The answer appears below with the calculated value, the formula used, and power dissipation when all three values are available.

Worked Example

You have a **12V battery** connected to a **24Ω resistor**. How much current flows?

Enter V = 12, R = 24, leave I empty Click Calculate **Result: I = 0.5A (500mA)**

Power dissipated: P = 12V × 0.5A = **6 Watts**

Pro Tips

  • Always use base units: Volts, Amps, and Ohms. Convert milliamps to amps (divide by 1000) and kilohms to ohms (multiply by 1000) before entering values.
  • If you enter all three values, the calculator will verify consistency and show total power dissipation.
  • Ohm’s Law only applies to resistive (linear) components. It does not directly apply to diodes, transistors, or other nonlinear devices.