Power Dissipation Calculator

Created: 18/03/2026Updated: 13/06/2026By: Mert
Power Dissipation Calculator
P = V × I
P = I²R
P = V²/R
Power Dissipation — Enter Any Two Values
V Voltage
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I Current
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Ω Resistance
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Enter any two values
Power Dissipation Results
Power
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W
Voltage
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V
Current
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A
Resistance
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Ω
Energy/hour
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Wh
Suggested Rating
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Power Dissipation: P = V × I I R V šŸ”„ Heat = P Power dissipated as heat: P = V×I = I²R = V²/R

Figure 1: Current flowing through resistance generates heat. The power dissipated must not exceed the component’s rating to prevent damage.

Table of Contents
Fundamentals
  1. What Is Power Dissipation?
  2. The Three Power Formulas
Worked Examples
  1. LED Resistor
  2. Voltage Regulator Heat
  3. Cable Losses
Deep Dive
  1. Component Power Ratings
  2. Thermal Management
Reference
  1. Frequently Asked Questions
  2. Related Circuit Analysis Calculators

What Is Power Dissipation?

Power dissipation is the rate at which a component converts electrical energy into heat. Every resistor, wire, transistor and IC dissipates some power as heat. If the heat cannot escape fast enough, the component overheats and may fail, change value, or catch fire. Understanding power dissipation is critical for reliable circuit design.

The Circuit Current Calculator finds the current flowing through components, which directly determines how much power they dissipate.

The Three Power Formulas

P = V × I (when you know voltage and current)
P = I² × R (when you know current and resistance)
P = V² / R (when you know voltage and resistance)
All three give the same answer — use whichever matches your known values.

Worked Example — LED Resistor

Given: V = 5 V across resistor, I = 20 mA, R = 250 Ω

P = 5 × 0.02 = 100 mW (0.1 W)

A standard ¼W (250 mW) resistor handles this with 60% margin.

The Series Circuit Calculator can find the voltage across the resistor in a series LED circuit.

Worked Example — Voltage Regulator Heat

Given: Vin = 12 V, Vout = 5 V, I = 500 mA

Vdrop = 12 − 5 = 7 V

P = 7 × 0.5 = 3.5 W — needs a heatsink!

Worked Example — Cable Losses

Given: Cable R = 0.275 Ω, I = 10 A

P = 10² × 0.275 = 27.5 W wasted as heat in the cable.

The Voltage Drop Calculator computes cable resistance from length, gauge and material, then the power loss follows directly.

Component Power Ratings

Standard through-hole resistors come in ⅛W, ¼W, ½W, 1W, 2W, 5W and 10W ratings. Always use at least 2× the calculated dissipation as the rating — this provides thermal margin and extends component life. SMD resistors have lower ratings due to their smaller size: 0402 (&frac1;16;W), 0603 (&frac1;10;W), 0805 (⅛W), 1206 (¼W).

Thermal Management

When power dissipation is high, heat must be removed actively: heatsinks increase the surface area for convection, thermal pads conduct heat to the PCB or chassis, and fans provide forced airflow. The junction temperature of a semiconductor is Tj = Tambient + P × θJA, where θJA is the junction-to-ambient thermal resistance. The Parallel Circuit Calculator can help design parallel resistor arrays to spread power dissipation across multiple components.

Frequently Asked Questions

Does a capacitor dissipate power?
An ideal capacitor stores and returns energy without dissipating any. Real capacitors have equivalent series resistance (ESR) that dissipates P = I² × ESR. This matters in switching power supplies and audio applications where ripple current is high.
What about inductors?
Ideal inductors store energy magnetically without dissipation. Real inductors have winding resistance (DCR) and core losses. Power dissipation = I² × DCR + core losses. Core losses increase with frequency.
How do I derate for temperature?
Most resistors are rated at 70°C ambient. Above this, the allowable power decreases linearly to zero at the maximum temperature (typically 155°C). In hot environments, use a higher-rated component or provide better cooling.
Can I parallel resistors to spread power?
Yes. Two identical resistors in parallel share the current equally, so each dissipates half the total power. Four in parallel each handle a quarter. This is a common technique for high-power applications using standard components.
What is the most efficient circuit?
Switching regulators (buck, boost) are far more efficient than linear regulators because they store and release energy rather than dissipating it. A linear regulator turning 12V to 5V wastes 58% as heat; a buck converter achieves 90%+ efficiency.
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Last updated: March 2026