Efficiency Calculator
Use our efficiency calculator to calculate percentage efficiency from energy input (J) and energy output (J). Includes the percent efficiency equation, how efficiency is calculated, and FAQs like can efficiency be over 100.
What Is Efficiency?
Efficiency describes how much useful output you get compared to what you put in. In energy terms, it compares useful energy output to total energy input.
Efficiency is commonly expressed as a percentage. Higher efficiency means less energy is wasted as heat, friction, sound, or other losses.
This calculator uses energy input (E_in) and energy output (E_out) in joules (J) to return efficiency (%).
Percentage Efficiency Formula
Percentage efficiency is output divided by input, multiplied by 100.
E_in must be greater than 0.
Multiply the ratio by 100 to convert to percent.
An 85% efficiency means 15% of the input energy was lost to non-useful forms.
How to Calculate Percentage Efficiency
- 1
Enter energy input (E_in) in joules (J).
- 2
Enter energy output (E_out) in joules (J).
- 3
The calculator computes (E_out ÷ E_in) × 100 to return efficiency (%).
Frequently Asked Questions
Efficiency is calculated as useful output divided by input. For percent efficiency: (E_out ÷ E_in) × 100.
Efficiency(%) = (E_out / E_in) × 100.
For a simple energy efficiency definition (useful output energy divided by input energy), efficiency above 100% usually indicates a measurement error, mismatched units, or that the system is drawing additional energy from an external source not counted in E_in.
Efficiency ratio (decimal) = E_out ÷ E_in. Multiply by 100 to convert it to percentage efficiency.
Divide output by input and multiply by 100. Example: output 80 J, input 100 J → 80%.