Energy Efficiency Calculator (η = Output/Input × 100)
Energy Efficiency Calculator (η = Output/Input × 100)
Efficiency measures how much of the energy put into a system comes out as useful energy, expressed as a percentage. Choose which quantity you want to solve for, enter the other two known values, and this calculator computes the missing one.
No real machine reaches 100% efficiency — some input energy is always lost along the way as heat, sound, or friction, which is a direct consequence of the second law of thermodynamics rather than simply an engineering limitation that better design could eventually eliminate entirely. This same efficiency formula applies identically across wildly different systems — a car engine converting fuel to motion, a light bulb converting electricity to light, a solar panel converting sunlight to electricity — which is exactly why "efficiency percentage" is such a universally useful comparison metric across otherwise unrelated technologies.
- The core formula is η = (Output ÷ Input) × 100, so a machine producing 75 J of useful output from 100 J of input energy is 75% efficient.
- No real machine is 100% efficient - some energy is always lost as heat, sound, or friction, which is why efficiency is always less than 100% in practice.
- This same formula applies to any energy conversion - engines, light bulbs, solar panels, and power plants are all commonly compared by their efficiency percentage.
How do I calculate efficiency?
Divide the useful energy output by the total energy input, then multiply by 100: η = (Output ÷ Input) × 100.
What is the efficiency of a machine that outputs 75 J from 100 J of input?
η = (75 ÷ 100) × 100 = 75%.
Energy Efficiency Calculator (η = Output/Input × 100)
Efficiency measures how much of the energy put into a system comes out as useful energy, expressed as a percentage. Choose which quantity you want to solve for, enter the other two known values, and this calculator computes the missing one.
No real machine reaches 100% efficiency — some input energy is always lost along the way as heat, sound, or friction, which is a direct consequence of the second law of thermodynamics rather than simply an engineering limitation that better design could eventually eliminate entirely. This same efficiency formula applies identically across wildly different systems — a car engine converting fuel to motion, a light bulb converting electricity to light, a solar panel converting sunlight to electricity — which is exactly why "efficiency percentage" is such a universally useful comparison metric across otherwise unrelated technologies.
- The core formula is η = (Output ÷ Input) × 100, so a machine producing 75 J of useful output from 100 J of input energy is 75% efficient.
- No real machine is 100% efficient - some energy is always lost as heat, sound, or friction, which is why efficiency is always less than 100% in practice.
- This same formula applies to any energy conversion - engines, light bulbs, solar panels, and power plants are all commonly compared by their efficiency percentage.
How do I calculate efficiency?
Divide the useful energy output by the total energy input, then multiply by 100: η = (Output ÷ Input) × 100.
What is the efficiency of a machine that outputs 75 J from 100 J of input?
η = (75 ÷ 100) × 100 = 75%.