Ohm's Law Calculator | Solve for V, I & R

Solve Ohm's Law (V=IR) for voltage, current, resistance, or power

Built-in unit conversions (mV, µA, kΩ) and power formulas for DC electrical circuit...

When Should You Use This Calculator?

Finding resistor value for LED current limiting (e.g., 5V supply, 20 mA)
Calculating current or power for automotive (12V) or mains (120V) circuits
Checking power dissipation to avoid overheating
Visualizing V/I/R/P relationships via the interactive Ohm's Law wheel

How to Use This Calculator

Choose what to solve for: voltage, current, resistance, or power.
Enter the other two known values.
Read all four values — the one you solved for plus the other three, computed automatically.
Use the interactive wheel to jump to a different solve-for quantity, or expand the formula reference for the underlying equations.

Key Features:

One unified screen — solve for voltage, current, resistance, or power
Unit support (m, μ, k, M) for all quantities
Interactive Ohm’s Law wheel embedded in every result for quick solve-target selection
Expandable formula reference (V=IR and all power forms) shown on demand
Copy results and export (JSON for guests; PDF/CSV when signed in)

Frequently Asked Questions

What is Ohm's Law?

Ohm's Law states that V = I × R (Voltage = Current × Resistance). It describes how current flows through a conductor proportional to voltage and inversely proportional to resistance.

How do I calculate power in a circuit?

Power (measured in Watts) can be calculated as P = V × I, P = I² × R, or P = V² / R. Our calculator provides all four power formulas automatically based on your known values.

What units do I use in Ohm's Law calculations?

Standard units: Voltage in Volts (V), Current in Amperes (A), Resistance in Ohms (Ω), Power in Watts (W). This calculator also accepts millivolts (mV), microamps (µA), kilohms (kΩ), and milliwatts (mW) — just select the unit prefix from the dropdown.

Can I use Ohm's Law for AC circuits?

Ohm's Law (V=IR) applies directly to DC circuits. For AC circuits, resistance becomes impedance (Z), which includes capacitive and inductive reactance. This calculator covers DC and resistive AC. Use the Power Calculator for AC phase angle and power factor analysis.

Can I export my Ohm's Law Calculator calculations?

Yes. In guest mode you can export your calculations to JSON. Signing in adds PDF and CSV export. Click the export button to download your results — useful for record-keeping, sharing, or importing into other tools.

Does this calculator save my history?

Yes. Your calculation history is saved automatically. As a guest you can keep up to 50 calculations per workspace on your device. Sign in for free to keep up to 100 per workspace and access them from any device.

Is this calculator free to use?

Yes. The Ohm's Law Calculator is free to use with no sign-up required. A free account adds more calculation history, multiple workspaces, and access to your saved data from any device.

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