Ohm

Calculate voltage, current, resistance, and power using Ohm This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.

How to Use the Ohm

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a Ohm?

An Ohm's Law Calculator solves for any electrical value — voltage (V), current (I), resistance (R), or power (P) — given the other two values. Ohm's Law (V = I × R) is the most fundamental relationship in electricity and electronics, as essential as arithmetic. This calculator is used by electricians, electronics engineers, students, and anyone working with circuits.

How Does It Work?

Enter any two known values: Voltage (volts), Current (amps), Resistance (ohms), or Power (watts). The calculator computes the other two values using Ohm's Law and the power formula (P = V × I). Results are shown instantly with the formulas applied, useful for learning. The interactive wheel diagram shows the relationships visually.

Formula

V = I × R (Voltage = Current × Resistance)\nI = V ÷ R | R = V ÷ I\nP = V × I (Power = Voltage × Current)\nP = I² × R | P = V² ÷ R\n\nWheel: V=IR, I=V/R, R=V/I, P=VI, P=I²R, P=V²/R

Who Uses This Tool?

• Electricians calculating circuit parameters during installation
• Electronics engineers designing circuits and selecting components
• Students learning foundational electrical principles
• Vapers calculating coil resistance for safe mod operation
• Audio engineers matching amplifier output to speaker impedance

Pro Tips

• The power triangle is just as important: P=VI. A 15A circuit at 120V can deliver 1800W maximum (less 20% safety margin = 1440W continuous)
• For AC circuits, use impedance (Z) instead of resistance (R) when inductors or capacitors are involved. Ohm's Law for AC: V = I × Z
• Always include a safety margin: if your calculation says 9.5A, size for 12-15A minimum. Electrical components should never run at 100% rated capacity

Frequently Asked Questions about Ohm

How are voltage, current, and resistance related?

Voltage (pressure pushing electrons) = Current (flow rate of electrons) × Resistance (opposition to flow). Double the voltage and current doubles; double the resistance and current halves.

What kills — voltage or current?

Current through the heart (~100-200mA can be fatal). But voltage drives current through body resistance. High voltage + enough energy = dangerous. Static electricity is thousands of volts but microamps — safe.

Free online Ohm — no signup, 100% client-side processing. All data stays in your browser.