Efficiency Calculator — Useful Output vs Total Input
Compute efficiency as the percentage of input energy converted to useful output, with an optional Carnot efficiency upper bound for heat engines.
K
K
Percentage of input energy converted to useful output
75 %
efficiencyUseful output
75%
Losses
25%
- 1
Efficiency ratio
75 ÷ 100 = 0.75 - 2
Efficiency η
0.75 × 100 = 75Percentage of input energy converted to useful output.
How does this calculator work?
Efficiency η = (useful output / total input) × 100 %. The Carnot limit η = (1 − T_c/T_h) × 100 % (temperatures in kelvin) is the maximum possible for any heat engine. Enter input and output to see efficiency and losses; add hot and cold temperatures to compare against the thermodynamic ceiling.
Formula
How this is calculated
Efficiency is the ratio of useful output to total input, expressed as a percentage. If a motor consumes 1 000 W and delivers 750 W of mechanical power, its efficiency is 75 % — the remaining 250 W is lost as heat, friction, or noise. The same formula applies to any energy conversion process: thermal engines, electrical transformers, pumps, lighting, or industrial plants. Inputs and outputs only need to be in the same units (watts, joules, kilowatt-hours, etc.).
For heat engines that convert heat into work, no real machine can exceed the Carnot efficiency: η_Carnot = (1 − T_c / T_h) × 100 %, where T_h and T_c are the temperatures of the hot source and cold sink in kelvin. This ceiling is set by the second law of thermodynamics and applies regardless of the working fluid or engine design. A steam turbine running between 800 K and 300 K has a Carnot limit of 62.5 %; practical turbines achieve 35–45 % due to irreversibilities such as friction, heat losses, and non-ideal gas behaviour.
Limitations: this calculator measures first-law (energy) efficiency — the ratio of energy quantities. It does not compute exergy (second-law) efficiency, which compares real performance to the thermodynamically ideal process, nor does it account for lifecycle energy, embodied carbon, or part-load performance. For systems where output is not of the same energy type as input (e.g. a solar panel converting radiation to electricity), convert to the same unit before entering values.
Frequently asked questions
Efficiency (η) is the ratio of useful output to total input and is a first-law thermodynamic concept. Effectiveness (ε) is used in heat-exchanger analysis (the ε–NTU method) and compares the actual heat transfer to the maximum theoretically possible for the given inlet conditions.
The second law of thermodynamics requires that some heat be rejected to the cold reservoir. Even the ideal (frictionless, reversible) Carnot engine achieves less than 100 % whenever T_c > 0 K. Real engines fall further short due to friction, heat leaks, and irreversible processes.
Yes — efficiency is dimensionless, so input and output must be in the same units. If your system converts between energy forms (electrical to mechanical, chemical to thermal), convert both to joules or watts before entering them.
Also known as
TG we-Calculate Editorial Team. (2026). Efficiency Calculator — Useful Output vs Total Input [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/efficiency-calculator
TG we-Calculate Editorial Team. "Efficiency Calculator — Useful Output vs Total Input." TG we-Calculate. 2026. https://we-calculate.com/calculator/efficiency-calculator.
TG we-Calculate Editorial Team, "Efficiency Calculator — Useful Output vs Total Input," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/efficiency-calculator
@misc{wecalculate_efficiency_calculator, title = {Efficiency Calculator — Useful Output vs Total Input}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/efficiency-calculator}}, year = {2026}, note = {TG we-Calculate} }
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