Calculate efficiency percentage, output, or input for any system or process. Free online efficiency calculator for engines, machines, energy systems, and more. Works with energy, power, and work calculations.
Calculate efficiency, output, or input for any system or process
Formula:
Efficiency = (Output ÷ Input) × 100%
The useful output produced by the system
The total energy/power/work put into the system
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Efficiency is one of the most important concepts in physics and engineering, representing how well a system converts input energy into useful output. Whether you're analyzing engine performance, evaluating energy systems, or optimizing processes, understanding efficiency is essential. Our Efficiency Calculator makes it easy to calculate efficiency percentage, output, or input for any system using the fundamental efficiency formula.
Efficiency is always expressed as a percentage, with 100% representing perfect efficiency (all input converted to useful output) and lower percentages indicating energy losses. In real-world systems, perfect efficiency is impossible due to friction, heat loss, and other factors. Our calculator helps you determine efficiency, calculate expected output based on efficiency, or determine required input to achieve desired output.
Our Efficiency Calculator offers three different calculation modes:
Select your calculation mode, enter the known values (using consistent units), and click Calculate to get instant results with detailed step-by-step solutions. The calculator works with any units—energy, power, work, or other quantities—as long as output and input use the same units.
The efficiency formula is fundamental to physics and engineering:
Efficiency = (Useful Output ÷ Total Input) × 100%
Where: Efficiency is expressed as a percentage (0% to 100%)
You can rearrange this formula to solve for any variable:
Different types of efficiency are used in various physics applications:
Efficiency calculations are essential in countless real-world scenarios:
Our Efficiency Calculator works with any units, as long as output and input use the same units:
Important: Always use consistent units for output and input. For example, if output is in watts, input must also be in watts. The calculator will give you the same efficiency percentage regardless of the units used (as long as they're consistent).
A gasoline engine produces 150,000 J of useful work from 500,000 J of fuel energy input. What is its efficiency?
Efficiency = (Output ÷ Input) × 100%
Efficiency = (150,000 J ÷ 500,000 J) × 100%
Efficiency = 0.30 × 100% = 30%
Energy lost = 500,000 J - 150,000 J = 350,000 J (70% lost as heat)
A solar panel with 22% efficiency receives 1,000 W of solar energy. What useful electrical power does it produce?
Output = (Input × Efficiency) ÷ 100%
Output = (1,000 W × 22%) ÷ 100%
Output = 220 W ÷ 1 = 220 W
Energy lost = 1,000 W - 220 W = 780 W (78% not converted to electricity)
An electric motor needs to produce 5 kW of mechanical power. If the motor is 85% efficient, what electrical power input is required?
Input = (Output × 100%) ÷ Efficiency
Input = (5 kW × 100%) ÷ 85%
Input = 500 ÷ 85 = 5.88 kW
Energy lost = 5.88 kW - 5 kW = 0.88 kW (15% lost as heat)
Real-world efficiency values vary widely by system type:
Note: Perfect efficiency (100%) is theoretically impossible in real systems due to the laws of thermodynamics and energy losses from friction, heat, sound, and other factors.
Understanding where energy is lost helps improve efficiency:
Improving efficiency often involves reducing these losses through better design, materials, maintenance, and system optimization.
Efficiency is the ratio of useful output to total input, expressed as a percentage. It's important because it measures how well a system converts input energy into useful output. Higher efficiency means less energy waste, lower operating costs, and better performance. Efficiency is crucial for comparing systems, optimizing designs, and reducing energy consumption.
No, efficiency cannot be greater than 100% in normal systems. Efficiency greater than 100% would violate the law of conservation of energy, as it would imply that more energy is produced than is put in. However, some systems like heat pumps have coefficients of performance (COP) greater than 1, which can be confusing—this is not true efficiency but rather a measure of heat transfer relative to work input.
You can use any units (energy, power, work) as long as output and input use the same units. Common units include joules, watts, kilowatt-hours, calories, or BTU. Efficiency is always expressed as a percentage. The key is consistency—output and input must use matching units for accurate calculations.
Improving efficiency typically involves reducing energy losses: minimize friction through better lubrication and design, reduce heat loss through insulation, optimize system design, use more efficient components, perform regular maintenance, and reduce unnecessary energy consumption. Each system type has specific optimization strategies.
Efficiency is the ratio of useful output to input (a quantitative measure), while effectiveness is how well a system achieves its intended purpose (a qualitative measure). A system can be efficient but not effective (produces output efficiently but doesn't meet requirements) or effective but not efficient (meets requirements but wastes energy).
Perfect efficiency is impossible due to the laws of thermodynamics, particularly the second law. Energy losses occur through friction, heat transfer, sound, vibration, and other unavoidable processes. Real systems always have some energy dissipation, making 100% efficiency a theoretical ideal that cannot be achieved in practice.
For systems in series, multiply individual efficiencies: Overall Efficiency = Efficiency₁ × Efficiency₂ × Efficiency₃ × ... For example, if a generator is 90% efficient and a motor is 85% efficient, the overall efficiency is 0.90 × 0.85 = 0.765 or 76.5%. Each system's losses compound, reducing overall efficiency.
Carnot efficiency is the maximum theoretical efficiency for a heat engine operating between two temperature reservoirs. It's given by: η = 1 - (T_cold / T_hot), where temperatures are in Kelvin. This represents the absolute maximum efficiency possible for any heat engine, and real engines always operate below this limit.
Efficiency is a fundamental concept in physics and engineering that measures how well systems convert input into useful output. Our Efficiency Calculator simplifies these calculations, making it easy to determine efficiency, calculate expected output, or determine required input for any system or process.
Ready to explore more physics concepts? Check out our other calculators like the Kinetic Energy Calculator for energy calculations, or the Watt Calculator for power calculations that often complement efficiency analysis.
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