Enter any two of the three values — Energy Input, Energy Output, or Efficiency (%) — and the Efficiency Calculator solves for the missing one. Whether you're analyzing a motor, engine, solar panel, or any mechanical system, you get the efficiency percentage, along with the energy lost as waste heat or friction.
Efficiency
--
Energy Input
--
Energy Output
--
Energy Lost (Waste)
--
Efficiency is the ratio of useful energy output to total energy input, expressed as a percentage. It measures how well a system converts input energy into useful work. A higher efficiency means less energy is wasted as heat, friction, or other losses.
Efficiency is calculated using the formula: η = (Energy Output / Energy Input) × 100%. For example, if a machine receives 1000 J of energy and produces 750 J of useful work, its efficiency is 75%. The remaining 25% (250 J) is lost as waste energy.
To find a machine's efficiency, divide its useful energy output by the total energy input, then multiply by 100 to get a percentage. You need to know two of the three values — input, output, or efficiency — and this calculator will solve for the third.
Efficiency is a dimensionless ratio and is typically expressed as a percentage (%). Since it represents the ratio of two quantities with the same unit (energy in and energy out), the units cancel out, leaving a pure number between 0% and 100%.
A machine with 60% efficiency converts 60% of its input energy into useful output work, while the remaining 40% is lost — typically as heat, sound, or friction. For instance, if you supply 500 J, only 300 J becomes useful work and 200 J is wasted.
No, a real machine cannot achieve 100% efficiency. Every physical system loses some energy to friction, heat, air resistance, or other irreversible processes. Only an ideal, theoretical machine (with no losses) could reach 100%, which is impossible in practice.
Carnot efficiency is the theoretical maximum efficiency of a heat engine operating between two temperature reservoirs. It is calculated as η = 1 − (T_cold / T_hot), where temperatures are in Kelvin. No real heat engine can exceed this limit, making it a fundamental benchmark in thermodynamics.
Efficiency calculations apply to electric motors, car engines, solar panels, power plants, light bulbs, refrigerators, and many other systems. Engineers use efficiency values to compare designs, reduce energy waste, lower operating costs, and meet environmental standards.