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Ohm's Law Calculator

Solve for voltage, current, resistance, or power given any two electrical values using Ohm's Law.

Select two known values and enter them below.

What is Ohm's Law Calculator?

The Ohm's Law Calculator solves for any one of the four fundamental electrical quantities — Voltage (V), Current (I), Resistance (R), and Power (P) — when you provide any two of them. It uses the relationships V = I × R and P = V × I.

How to use

  1. 1 Select the two values you already know from the first two dropdowns.
  2. 2 Enter the numeric values for those two quantities.
  3. 3 Click Calculate to solve for all four values.
  4. 4 The results show Voltage (V), Current (A), Resistance (Ω), and Power (W).
  5. 5 Use this for circuit design, troubleshooting, or selecting fuses and wire gauges.

Formula

V = I × R. I = V / R. R = V / I. P = V × I = I² × R = V² / R.

Example calculation

Know voltage (12 V) and resistance (6 Ω): I = 12 / 6 = 2 A. P = 12 × 2 = 24 W.

Frequently asked questions

What is Ohm's Law?

Ohm's Law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = I × R.

What units are used?

Voltage in Volts (V), Current in Amperes (A), Resistance in Ohms (Ω), and Power in Watts (W).

Does Ohm's Law apply to AC circuits?

Ohm's Law applies directly to resistive AC circuits. For circuits with capacitors or inductors, impedance (Z) replaces resistance.

Can I use milliamps or kilohms?

Enter all values in base units (amps, ohms, volts). Convert first: 50 mA = 0.05 A, 4.7 kΩ = 4700 Ω.

What if resistance is zero?

Zero resistance means a short circuit — current would theoretically be infinite. The calculator will flag this as an invalid input.