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Physics

Ohm's Law Calculator

Calculate voltage, current, resistance, and power

How to Use

Ohm's Law: V = I × R

Power: P = V × I

  • V = Voltage (Volts)
  • I = Current (Amperes)
  • R = Resistance (Ohms)
  • P = Power (Watts)

Enter any 2 values to calculate the third.

How to Use Ohm's Law Calculator

Ohm's Law is fundamental to electrical engineering and describes the relationship between voltage, current, resistance, and power. This calculator solves Ohm's Law and power equations instantly.

  1. Calculate voltage from current and resistance.
  2. Find current given voltage and resistance.
  3. Determine resistance from voltage and current.
  4. Calculate electrical power consumption.
  5. Analyze circuit behavior and efficiency.

Ohm's Law & Power Formulas

Understanding electrical relationships helps you design circuits, troubleshoot problems, and ensure safe operation.

Ohm's Law

V = I × R

Voltage equals current multiplied by resistance.

Example:

Input: Current: 2 Amps, Resistance: 10 Ohms

Calculation: 2 × 10

Result: 20 Volts

Current

I = V / R

Current equals voltage divided by resistance.

Example:

Input: Voltage: 120V, Resistance: 12Ω

Calculation: 120 ÷ 12

Result: 10 Amps

Resistance

R = V / I

Resistance equals voltage divided by current.

Example:

Input: Voltage: 48V, Current: 4A

Calculation: 48 ÷ 4

Result: 12 Ohms

Power

P = V × I or P = I² × R or P = V² / R

Power is the rate of energy consumption in watts.

Example:

Input: Using P = V × I: Voltage 120V, Current 10A

Calculation: 120 × 10

Result: 1200 Watts

Real-World Use Cases

Ohm's Law is used daily by electricians, engineers, and hobbyists working with electrical circuits and systems.

Home Electrical Safety

Check if your circuit breakers are properly sized and prevent overloads that could cause fires.

LED and Resistor Selection

Calculate the correct resistor values to limit current and protect LEDs in electronic projects.

Power Consumption Calculation

Determine how much electricity appliances use to estimate monthly electric bills.

Circuit Design & Troubleshooting

Verify circuit calculations during design phase and diagnose problems in existing circuits.

Industrial Motor Analysis

Calculate motor specifications, efficiency, and power requirements for industrial applications.

Tips & Best Practices

Tips

  • Remember: V = IR (Voltage equals current times resistance).
  • Resistance increases with wire length and decreases with larger wire diameter.
  • Power dissipation as heat increases with resistance and current.
  • Use appropriate wire gauge to handle current without dangerous heat generation.
  • Insulators have very high resistance; conductors have very low resistance.

Common Mistakes to Avoid

  • Forgetting that resistance changes with temperature in many materials.
  • Not accounting for voltage drop across long wire runs.
  • Confusing AC and DC calculations - Ohm's Law applies to DC and AC RMS values.
  • Ignoring power ratings and causing component overheating or failure.