Ohm's Law Calculator

⚡ Full Circuit Values

Voltage (V)–
Current (I)–
Resistance (R)–
Power (P)–

What Is Ohm's Law?

Ohm's Law describes the relationship between voltage, current, and resistance in an electrical circuit. This calculator solves for any missing value when you know the other two, and also calculates power.

How to Use the Ohm's Law Calculator

  1. Enter any two of the three values: voltage, current, or resistance.
  2. Leave the third field at 0 (or blank).
  3. The missing value and power are calculated instantly.

Ohm's Law Formulas

Ohm's Law
V = I × R
V = voltage (volts)
I = current (amps)
R = resistance (ohms)
Power
P = V × I = I² × R = V² / R
P = power (watts)

Worked Example

Example: 12V, 2A

Resistance: R = V/I = 12/2 = 6Ω

Power: P = V×I = 12×2 = 24W

Understanding Your Results

Ohm's Law is fundamental to circuit design and troubleshooting. Knowing any two values (voltage, current, or resistance) lets you find the third, and power calculations show how much energy the circuit consumes or dissipates.

Common Uses

  • Basic electronics and circuit design.
  • Selecting appropriately rated resistors for a circuit.
  • Troubleshooting unexpected voltage drops or current draws.
  • Educational reference for physics and electrical engineering students.

Common Mistakes to Avoid

  • Mixing up units (milliamps vs. amps, kilohms vs. ohms) without converting first.
  • Applying Ohm's Law to non-ohmic components (like diodes) where the relationship isn't linear.
  • Forgetting that power dissipated as heat can exceed a component's rating, risking damage.

Frequently Asked Questions

Ohm's Law states that voltage equals current multiplied by resistance (V = I × R), describing the fundamental relationship in electrical circuits.

Power (in watts) equals voltage times current (P = V × I), or equivalently I²R or V²/R, depending on which values you know.

Current decreases proportionally, since I = V/R — higher resistance restricts current flow for the same voltage.

It applies to "ohmic" components like resistors, where the voltage-current relationship is linear. Some components (diodes, transistors) are non-ohmic and don't follow this simple linear relationship.

Voltage in volts (V), current in amps (A), resistance in ohms (Ω), and power in watts (W) — the standard SI units for electrical calculations.