Ohm's Law Calculator

Calculate voltage, current, resistance, and power using Ohm's Law. Free electrical engineering calculator.

What is Ohm's Law Calculator?

Ohm's Law is a fundamental principle in electrical engineering and physics that describes the relationship between voltage, current, resistance, and power in an electrical circuit. Named after German physicist Georg Ohm, this law is the foundation for understanding how electrical circuits work and is essential for anyone working with electronics.

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. This simple relationship allows you to calculate any one of these values if you know the other two, making it an indispensable tool for circuit design, troubleshooting, and analysis.

Formula

V = I × R (Voltage = Current × Resistance)

I = V / R (Current = Voltage ÷ Resistance)

R = V / I (Resistance = Voltage ÷ Current)

P = V × I (Power = Voltage × Current)

Where: V = Volts, I = Amperes, R = Ohms, P = Watts

How to Calculate

Select which value you want to calculate (voltage, current, resistance, or power).
Enter the two known values in the corresponding fields.
The calculator computes the unknown value instantly.
View the power dissipation as a bonus calculation.
Use the results for circuit design or troubleshooting.

Example

A circuit has a 12V battery connected to a 4Ω resistor. To find the current: I = V/R = 12/4 = 3 amperes. The power dissipated by the resistor: P = V × I = 12 × 3 = 36 watts. This means the resistor must be rated for at least 36 watts to avoid overheating.

Key Benefits

Calculate voltage current resistance power instantly
Solve unknown electrical values from two known
Verify circuit designs for safety compliance
Multiple power formulas complete analysis

Common Mistakes to Avoid

AC DC confusion Ohm Law direct DC not AC
Forgetting unit conversions milliamp to amp
Wrong power formula incorrect wattage

Pro Tips

Ohm Law triangle V over I times R
Check power against component rated wattage
Series current constant voltage divides

Key Terms Explained

Voltage V: Electrical potential volts
Current I: Charge flow amperes
Resistance R: Opposition ohms
Power P: Energy transfer rate watts

When to Use This Calculator

Designing or troubleshooting circuits
Selecting components for requirements
Calculating safe power dissipation

Common Use Cases

Designing electrical circuits for electronics projects
Troubleshooting household electrical problems
Sizing resistors and components for LED circuits
Understanding power consumption of electrical devices

Frequently Asked Questions

What does Ohm's Law tell us?

Ohm's Law describes the relationship between voltage, current, and resistance in an electrical circuit. It states that current is directly proportional to voltage and inversely proportional to resistance.

When doesn't Ohm's Law apply?

Ohm's Law applies to ohmic materials (like most metals) at constant temperature. It doesn't apply to semiconductors, diodes, transistors, or materials where resistance changes with voltage or temperature.

How is power related to Ohm's Law?

Electrical power (P = V × I) can be combined with Ohm's Law to give P = I²R or P = V²/R. These formulas help calculate how much energy a component dissipates as heat.

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