Resistor Heat Calculator (Joule’s Law)

Calculate Power dissipation and heat generation in Resistors using Joule’s Law: P = I² × R.

How to use

Enter:

• Resistance (Ω) - The Resistor value
• Current (A) - The Current flowing through the Resistor

The calculator shows:

• Power (W) - Power dissipated as heat
• Heat warning - Whether the Resistor can handle the Power

Examples

Standard 1/4W Resistor

• Resistance: 220Ω
• Current: 20mA (0.02A)
• Power: 0.088W - Safe for 1/4W Resistor

High Power Application

• Resistance: 10Ω
• Current: 500mA (0.5A)
• Power: 2.5W - Needs 3W or 5W Resistor

FAQ

Q: Why do Resistors get hot? A: Resistors convert electrical Power into heat. The Power dissipated is P = I² × R.

Q: What happens if I exceed the Power rating? A: The Resistor will overheat, potentially causing failure, fire, or damage to nearby components.

Q: How do I choose the right Power rating? A: Always use a Resistor rated for at least 2× the calculated Power for safety margin.