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Ohm's Law CalculatorCalculate voltage, current, resistance, or power using Ohm's Law and the power equation.

Ohm's Law Calculator illustration
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Ohm's Law Calculator

Calculate voltage, current, resistance, or power using Ohm's Law and the power equation.

How to Use
1

Choose What to Solve

Select which value to calculate: voltage, current, resistance, or power.

2

Enter Known Values

Input any two of the remaining three values.

3

View Results

See all four values calculated with appropriate unit prefixes.

What Is Ohm's Law Calculator?

The Ohm's Law Calculator solves for any of the four fundamental electrical quantities — voltage (V), current (I), resistance (R), and power (P) — given any two known values. It combines Ohm's Law (V = I × R) with the power equation (P = V × I) to provide a complete set of results. The calculator automatically handles unit prefixes (mA, kΩ, MW, etc.) for easy reading. This is an essential tool for electrical engineers, electronics hobbyists, and students working with circuits.

Why Use Our Ohm's Law Calculator?

  • Solves for any of 4 values: voltage, current, resistance, power
  • Combines Ohm's Law and power equations in one calculator
  • Automatic unit prefix formatting (mA, kΩ, MW, etc.)
  • Accepts any two inputs to calculate the remaining values

Common Use Cases

Circuit Design

Calculate component values for electronic circuit design.

Electrical Safety

Determine current flow and power dissipation in circuits.

Education

Solve Ohm's Law problems for physics and engineering courses.

Troubleshooting

Verify expected values when diagnosing electrical issues.

Technical Guide

Ohm's Law: V = I × R. Power equations: P = V × I = I²R = V²/R. From any two known quantities, all four can be derived. Solving for each: V = IR, V = P/I, V = √(PR). I = V/R, I = P/V, I = √(P/R). R = V/I, R = V²/P, R = P/I². P = VI, P = I²R, P = V²/R. The calculator accepts inputs in base units (V, A, Ω, W) and displays results with appropriate SI prefixes: micro (μ), milli (m), kilo (k), mega (M). Ohm's Law applies to resistive (ohmic) circuits; reactive components (capacitors, inductors) require complex impedance calculations.

Tips & Best Practices

  • 1
    Always double-check units — mixing mA with V gives results in kΩ, not Ω
  • 2
    Power dissipation in resistors determines required wattage rating
  • 3
    Ohm's Law applies to DC circuits; AC circuits need impedance calculations
  • 4
    In series circuits, current is the same; in parallel, voltage is the same

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Frequently Asked Questions

QWhat is Ohm's Law?
Ohm's Law states that voltage equals current times resistance: V = I × R. It is the fundamental relationship governing electrical circuits.
QDoes Ohm's Law apply to all components?
Ohm's Law applies to ohmic (resistive) components. Non-ohmic components like diodes, transistors, and LEDs have non-linear V-I relationships.
QWhat units should I use?
Use base SI units: Volts (V), Amperes (A), Ohms (Ω), Watts (W). The calculator will format results with appropriate prefixes.
QHow do I calculate power?
Power = Voltage × Current (P = V × I). Alternatively: P = I²R or P = V²/R.
QWhat is the relationship between V, I, R, and P?
V = IR, P = VI. Given any two of the four quantities, the other two can be calculated using these relationships.

About Ohm's Law Calculator

Ohm's Law Calculator is a free online tool from FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration required. No ads. Just fast, reliable tools.