Power Dissipation Calculator
Calculate watt loss in a resistor, load, or component from voltage, current, or resistance, then compare the result with component rating and derating limits.
Engineering tool
Power Dissipation Calculator
Calculate component watt loss and compare it with derated power-rating limits.
Result console
- Calculated power
- 12W
- Recommended minimum rating
- 15W
- Derated allowable power
- 16W
- Power margin
- 8W
Power rating status
Safe
P = V × I
The calculated loss is within the derated rating. Verify worst-case electrical and thermal conditions.
Formula reference
Power Dissipation Formulas
Use the formula matching the two known electrical quantities.
P = V × IP = I² × RP = V² / RRecommended minimum rating = P / derating factorVariable definitions
- P
- dissipated power in watts
- V
- voltage across the component
- I
- current through the component
- R
- component resistance
Worked Example
At 12 V and 1 A, P = 12 × 1 = 12 W.
At 1 A through 10 Ω, P = 1² × 10 = 10 W.
At 12 V across 10 Ω, P = 12² / 10 = 14.4 W.
Engineering Notes
- Power dissipation becomes heat in the component.
- Resistors and semiconductors should be derated below maximum power rating.
- Temperature, airflow, PCB copper, and package size affect real thermal performance.
- I²R loss rises quickly with current.
- Use worst-case voltage and current for reliable design.
Support reference
FAQ
How do you calculate power dissipation?
Use P = VI when voltage and current are known, P = I²R for current through resistance, or P = V²/R for voltage across resistance.
What is I²R loss?
I²R loss is heat produced when current flows through resistance. Because current is squared, a small current increase can produce a much larger loss.
Why should power ratings be derated?
Derating keeps components below absolute maximum ratings and provides margin for temperature, tolerance, airflow, PCB layout, aging, and transient conditions.
What happens if power dissipation exceeds the rating?
The component may overheat, drift, shorten its life, damage nearby materials, or fail. Select a higher rating or reduce the electrical and thermal stress.
Is power dissipation the same as heat?
In resistive and semiconductor losses, dissipated electrical power is converted primarily into heat that must leave through the package, PCB, heatsink, and airflow.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
Engineering Guide
Power Dissipation and Component Power Ratings
Calculate actual component dissipation and choose safe power ratings using thermal resistance, derating, junction temperature, SOA, pulse conditions, PCB heat spreading, and real operating conditions.
20 min · Intermediate
Engineering Blog
10 Common Power Design Mistakes (and How to Avoid Them)
Avoid power design mistakes involving watts versus watt-hours, unit prefixes, RMS current, AC power factor, efficiency, derating, thermal design, startup current, voltage drop, batteries, PCB copper, and undersized components.
17 min · Intermediate
Engineering Guide
Understanding Electrical Power
Learn electrical power fundamentals, including voltage, current, resistance, watts, energy, Ohm's law, DC and AC power, efficiency, power dissipation, and practical calculations.
18 min · Beginner
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