Efficiency Calculator
Calculate power conversion efficiency, required input power, available output power, and heat-producing loss for supplies, regulators, converters, and electronic loads.
Engineering tool
Efficiency Calculator
Calculate power-stage efficiency, input power, output power, and power loss.
Result console
- Efficiency
- 90%
- Input power
- 120W
- Output power
- 108W
- Power loss
- 12W
Efficiency status
Good
Efficiency = Pout / Pin × 100%
Efficiency is suitable for many designs. Include the calculated loss in thermal sizing.
Formula reference
Efficiency Formulas
Efficiency is expressed as a decimal in equations and as a percentage in results.
Efficiency = Pout / Pin × 100%Power loss = Pin - PoutPin = Pout / EfficiencyPout = Pin × EfficiencyVariable definitions
- Pin
- input power
- Pout
- useful output power
- Ploss
- converted heat and other losses
Worked Example
Pin = 120 W and Pout = 108 W.
Efficiency = 108 / 120 × 100% = 90%.
Power loss = 120 - 108 = 12 W.
Engineering Notes
- Efficiency compares useful output power with input power.
- Power loss becomes heat and affects thermal design.
- Higher efficiency reduces cooling requirements.
- Converter efficiency varies with load, voltage, and switching frequency.
- Always use worst-case operating conditions for power and thermal sizing.
Support reference
FAQ
How do you calculate efficiency?
Divide useful output power by input power and multiply by 100 percent: efficiency = Pout / Pin × 100%.
What is power loss?
Power loss is the difference between input and output power. It is primarily converted into heat in the converter or load.
Why is efficiency important?
Higher efficiency reduces wasted energy, heat, cooling requirements, input-current demand, and operating cost.
Is 90% efficiency good?
Ninety percent is good for many power designs, but suitability depends on topology, power level, cooling, size, and operating range.
Why does efficiency change with load?
Fixed control and gate-drive losses dominate at light load, while conduction and magnetic losses grow with current. Voltage, frequency, and temperature also change losses.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
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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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
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.
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