How to Convert Kilowatt-Hours
Understanding Your Electricity Usage
Get the FormulasThe kilowatt-hour (kWh) is how electricity is measured and billed worldwide. Whether you're calculating appliance costs, comparing energy sources, or sizing a solar system, understanding how to convert kWh to other energy units is essential.
Understanding Kilowatt-Hours
A kilowatt-hour is not a rate—it's an amount of energy. It equals:
- 1,000 watts of power used for 1 hour
- 100 watts used for 10 hours
- 10 watts used for 100 hours
Formula: Energy (kWh) = Power (kW) × Time (hours)
A 100-watt (0.1 kW) light bulb running for 10 hours uses 1 kWh.
Conversion to Other Units
| Convert From | To | Multiply By |
|---|---|---|
| kWh | Joules (J) | 3,600,000 |
| kWh | Megajoules (MJ) | 3.6 |
| kWh | BTU | 3,412 |
| kWh | Calories (cal) | 860,420 |
| kWh | Kilocalories (kcal) | 860 |
| kWh | Watt-hours (Wh) | 1,000 |
| kWh | Therms | 0.0341 |
Reverse Conversions
| Convert From | To kWh | Divide By |
|---|---|---|
| Joules | kWh | 3,600,000 |
| MJ | kWh | 3.6 |
| BTU | kWh | 3,412 |
| Therm | kWh | 0.0341 (or × 29.3) |
Step-by-Step Examples
Example 1: kWh to Joules
Convert 5 kWh to joules:
- Use formula: Joules = kWh × 3,600,000
- Calculate: 5 × 3,600,000 = 18,000,000 J (18 MJ)
Example 2: kWh to BTU
Convert 10 kWh to BTU:
- Use formula: BTU = kWh × 3,412
- Calculate: 10 × 3,412 = 34,120 BTU
Example 3: BTU to kWh
Convert 100,000 BTU to kWh:
- Use formula: kWh = BTU ÷ 3,412
- Calculate: 100,000 ÷ 3,412 = 29.3 kWh
Common Appliance Energy Usage
| Appliance | Power (Watts) | Hours/Day | kWh/Day | kWh/Month |
|---|---|---|---|---|
| LED bulb | 10 W | 5 | 0.05 | 1.5 |
| Refrigerator | 150 W avg | 24 | 3.6 | 108 |
| TV (55") | 100 W | 4 | 0.4 | 12 |
| Laptop | 50 W | 6 | 0.3 | 9 |
| Air conditioner | 1,500 W | 8 | 12 | 360 |
| Electric water heater | 4,000 W | 3 | 12 | 360 |
| EV charging | 7,000 W | 4 | 28 | 840 |
Energy Equivalents
To put 1 kWh in perspective:
| 1 kWh Can... | Equivalent |
|---|---|
| Run a 100W bulb | 10 hours |
| Run a laptop | 20 hours |
| Watch TV (55") | 10 hours |
| Run a microwave (1000W) | 1 hour |
| Drive an electric car | 3-4 miles |
| Heat water | ~1 gallon from cold to hot |
kWh in Context: Fuel Comparisons
| Energy Source | Energy Content | Equivalent kWh |
|---|---|---|
| 1 gallon gasoline | ~121 MJ | ~33.7 kWh |
| 1 gallon diesel | ~137 MJ | ~38 kWh |
| 1 therm natural gas | ~105.5 MJ | ~29.3 kWh |
| 1 kg coal | ~24 MJ | ~6.7 kWh |
| 1 kg wood | ~16 MJ | ~4.4 kWh |
Conclusion
The kilowatt-hour is the standard unit for measuring electrical energy consumption. Converting to joules (multiply by 3,600,000) or BTU (multiply by 3,412) allows comparison with other energy sources and calculations. Understanding kWh helps you estimate costs, size renewable energy systems, and make informed energy decisions.