⚡ Power Dissipation Calculator
Calculate power dissipated in resistors
How to Use This Calculator
Select Calculation Method
Choose the method based on which values you know: Voltage & Current (P = V × I), Current & Resistance (P = I² × R), or Voltage & Resistance (P = V² / R).
Enter Known Values
Input the values you know. The calculator will show only the relevant input fields based on your selected method.
Calculate
Click the "Calculate Power Dissipation" button to get the power dissipated in Watts. This represents the power lost as heat in the resistor.
Formula
P = V × I
Using Voltage and Current
P = I² × R
Using Current and Resistance
P = V² / R
Using Voltage and Resistance
Where:
- P = Power Dissipated (Watts, W)
- V = Voltage (Volts, V)
- I = Current (Amperes, A)
- R = Resistance (Ohms, Ω)
Example Calculation:
For a resistor with I = 2 A, R = 10 Ω:
P = I² × R = 2² × 10 = 4 × 10 = 40 W
Note: Power dissipation represents energy converted to heat per second. All three formulas are equivalent and can be derived from each other using Ohm's law (V = I × R).
About Power Dissipation Calculator
The Power Dissipation Calculator determines the power lost as heat when current flows through a resistor. Power dissipation is a critical parameter in circuit design, as it determines resistor sizing, thermal management requirements, and circuit efficiency. All three calculation methods (P = VI, P = I²R, P = V²/R) are equivalent and interchangeable using Ohm's law.
When to Use This Calculator
- Circuit Design: Determine power ratings needed for resistors
- Thermal Analysis: Calculate heat generation in electronic circuits
- Component Selection: Select appropriate resistor power ratings
- Power Analysis: Analyze power consumption and losses
- Safety Design: Ensure components operate within safe power limits
Why Use Our Calculator?
- ✅ Multiple Methods: Three calculation methods for different known values
- ✅ Quick Calculation: Instantly determine power dissipation
- ✅ Component Sizing: Essential for proper resistor selection
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Learn about power dissipation and heat generation
Common Applications
Resistor Selection: Calculate power dissipation to select resistors with appropriate power ratings. Resistors must be rated for at least the calculated power (with safety margin). Common ratings include 1/8W, 1/4W, 1/2W, 1W, and higher. Exceeding power rating causes overheating and failure.
Heat Management: Determine heat generation in circuits for thermal design. Power dissipation represents energy converted to heat per second. High-power resistors require heat sinks or forced cooling. This calculator helps design thermal management systems to prevent component damage.
Circuit Efficiency: Calculate power losses to analyze circuit efficiency. In power conversion circuits, power dissipation in resistors represents energy loss. Understanding these losses helps optimize circuit design for better efficiency, important in battery-powered and energy-efficient systems.
Tips for Best Results
- Always use resistors rated for at least 2× calculated power for safety margin
- Power dissipation increases with square of current (P = I²R)
- High-power applications may require heat sinks or forced cooling
- Consider derating at high temperatures (resistors lose power rating with temperature)
- For AC circuits, use RMS values for voltage and current
Frequently Asked Questions
What is power dissipation?
Power dissipation is the power lost as heat when current flows through a resistor. It's the rate at which electrical energy is converted to thermal energy. Power dissipation is calculated using P = VI, P = I²R, or P = V²/R, all of which are equivalent.
Why does power dissipation matter?
Power dissipation determines how much heat a resistor generates. If power exceeds the resistor's rating, it will overheat and fail. Power dissipation also affects circuit efficiency - higher dissipation means more energy wasted as heat. Proper power rating selection ensures reliable operation.
How do I select the right resistor power rating?
Calculate the power dissipation and select a resistor rated for at least 2× that value (safety margin). For example, if dissipation is 0.5W, use a 1W or higher resistor. Standard ratings are 1/8W, 1/4W, 1/2W, 1W, 2W, 5W, 10W, etc. Higher power means larger physical size.
Why does power increase with current squared?
From P = I²R, power is proportional to current squared because both voltage drop (V = IR) and current increase with current. Doubling current quadruples power dissipation. This is why current-limiting circuits and fuses are important - small current increases cause significant power and heat increases.
Can I use these formulas for AC circuits?
Yes, but use RMS (root mean square) values for voltage and current. For AC, P = VRMS × IRMS = I²RMS × R = V²RMS / R. RMS values represent the equivalent DC values that produce the same power dissipation.
What happens if I exceed the resistor power rating?
Exceeding power rating causes the resistor to overheat, which can lead to: resistance value drift, physical damage (burning, cracking), complete failure (open circuit), or in extreme cases, fire. Always design with adequate safety margins and proper heat management.