Efficiency Calculator

This calculator works out efficiency, the percentage of energy or power that a machine or process turns into useful output rather than wasting. No real device is perfect: some of the energy you put in always ends up as unwanted heat, sound, friction or other losses, and efficiency measures how much actually does the job you want. It is one of the most important figures in engineering and energy, used to compare engines, motors, appliances, power stations, light bulbs and entire processes, and to identify where energy, and money, is being wasted. Efficiency is simply the useful output divided by the total input, expressed as a percentage, and because output can never exceed input, it is always less than 100 percent. This tool computes it. You enter the useful energy or power that comes out and the total energy or power that goes in, in the same units, and the calculator returns the efficiency as a percentage, the percentage wasted, and the amount of energy or power lost. The results update as you type. Use it to rate the efficiency of a device or process, to compare options, to quantify waste, or for physics and engineering study. The principle is universal and the units cancel, so it works for energy in joules, power in watts, or any consistent measure of input and output. Some context for the numbers: an incandescent light bulb is only a few percent efficient at producing light, a petrol car engine around a quarter to a third, an electric motor often over 90 percent, and a good heat pump can appear to exceed 100 percent of its electrical input because it moves existing heat rather than generating it, though that is a coefficient of performance rather than true efficiency. For ordinary energy conversion, a figure above 100 percent signals an error in the inputs.

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Efficiency = useful output / total input x 100. Use the same units for both. Efficiency is always under 100% for real energy conversion; over 100% means an input error.