Efficiency tells you how much of the energy put into a device comes out as useful energy. This efficiency calculator divides the useful output by the total input and gives a percentage.
Use energy (joules) or power (watts) — the units just need to match. No real machine is 100% efficient: some energy is always lost, mostly as heat.
| Useful output energy or power | 450 |
| Total input energy or power | 600 |
| Efficiency (%) | 75% |
| Energy or power wasted (same unit) | 150 |
| Wasted (%) | 25% |
A motor giving 450 W of mechanical power from 600 W of electricity is 75% efficient.
Try this example →| Useful output energy or power | 5 |
| Total input energy or power | 100 |
| Efficiency (%) | 5% |
| Energy or power wasted (same unit) | 95 |
| Wasted (%) | 95% |
A 100 W bulb giving 5 W of light is only 5% efficient; the rest is heat.
Try this example →Efficiency = useful output ÷ total input × 100%.
No. That would mean creating energy, which breaks the law of conservation of energy.
Mostly into heat, and some into sound and vibration.
No. It is a ratio, usually written as a percentage.