What Are Energy and Consumption? (Wh / kWh)
Electrical energy is power multiplied by time, usually measured in watt-hours (Wh) or kilowatt-hours (kWh). One kWh is the energy used by 1000 watts running for one hour. Electricity bills are calculated in kWh. The relation Energy = Power × Time is the basis for working out consumption.
Energy is power accumulated over time: Energy = Power × Time. Its unit is the watt-hour (Wh), or on a large scale the kilowatt-hour (kWh). This energy is also what you pay for on your electricity bill.
The Difference Between Power and Energy
The two are often confused but are different: power (W) is the instantaneous rate — "how much is it using right now?" Energy (Wh) is the total — "how much did it use over time?" A 100 W bulb burning for 10 hours consumes 100 × 10 = 1000 Wh = 1 kWh of energy.
Units
| Unit | Meaning | Example |
|---|---|---|
| Wh | Watt-hour | A 1 W device running 1 hour = 1 Wh |
| kWh | 1000 Wh | The unit on your bill |
| mAh | Milliampere-hour | Battery capacity (depends on voltage) |
Battery Capacity: mAh and Wh
Battery capacity is usually given in mAh; but to find the real energy you have to multiply by the voltage. For example, a 2000 mAh (2 Ah), 3.7 V LiPo battery holds: Energy = 2 Ah × 3.7 V = 7.4 Wh.
Worked Example: Runtime
With a 7.4 Wh battery, a device drawing an average of 0.5 W theoretically runs for 7.4 / 0.5 = 14.8 hours (a bit less in practice due to losses).
Common Mistakes
- Treating mAh as energy directly: mAh alone isn't energy; you can't get Wh without multiplying by voltage.
- Confusing power with energy: 100 W ≠ 100 Wh; one is a rate, the other a total amount.
- Comparing batteries of different voltages by mAh: 2000 mAh @ 3.7 V and 2000 mAh @ 1.2 V don't have the same energy.
Frequently Asked Questions
What is a kWh?+
How do you calculate energy?+
What's the difference between power and energy?+
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