Efficiency Formula
Calculate how effectively a system converts input energy to useful output.
Applies to engines, motors, and any energy system.
The Formula
η = (Useful Output / Total Input) × 100%
Efficiency measures the percentage of input energy that becomes useful output. No real system is 100% efficient — some energy is always lost to heat, friction, or other waste.
Variables
| Symbol | Meaning |
|---|---|
| η | Efficiency (percentage, 0-100%) |
| Useful Output | Energy or power that does the intended work (joules or watts) |
| Total Input | Total energy or power supplied to the system (joules or watts) |
Example 1
A motor consumes 500 W and produces 400 W of mechanical power
η = (400 / 500) × 100%
η = 80% (100 W lost as heat)
Example 2
A car engine burns fuel with 30,000 J of energy and delivers 9,000 J to the wheels
η = (9,000 / 30,000) × 100%
η = 30% (typical for internal combustion engines)
When to Use It
Use the efficiency formula when:
- Comparing the performance of different machines or engines
- Calculating energy waste and operating costs
- Evaluating renewable energy systems (solar panels, wind turbines)
- Identifying where energy improvements will have the biggest impact