Kilowatt-hours to joules (kWh to J) converter

What is a kilowatt-hours to joules converter?

A kilowatt-hours to joules converter is an online tool that turns an amount of energy expressed in kilowatt-hours (kWh) into its equivalent in joules (J), and vice versa. The kilowatt-hour is the unit most people see on their electricity bills, while the joule is the base unit of energy in the International System of Units (SI). Because the two units describe the same physical quantity at vastly different scales, having a quick way to move between them is useful for anyone working with electricity, physics, or engineering data.

How does the converter work?

Both quantities measure energy, so the conversion is a single fixed factor. One watt is one joule per second, and one kilowatt is 1,000 watts. Running 1,000 watts for one full hour (3,600 seconds) therefore delivers:

$1\,000 \text{ W} \times 3\,600 \text{ s} = 3\,600\,000 \text{ J}$

So one kilowatt-hour equals exactly 3,600,000 joules (3.6 megajoules). The converter applies this factor automatically: type a value into either field and the other side updates instantly. You can also switch units on either side, choosing among kilowatt-hours, joules, kilojoules, megajoules, and calories, and the tool keeps both fields in step.

Formula for conversion

To convert kilowatt-hours to joules, multiply by 3,600,000:

$\text{J} = \text{kWh} \times 3\,600\,000$

To convert joules back to kilowatt-hours, divide by 3,600,000:

$\text{kWh} = \frac{\text{J}}{3\,600\,000}$

It is sometimes handier to work in kilojoules (kJ) or megajoules (MJ):

$\text{kJ} = \text{kWh} \times 3\,600$

$\text{MJ} = \text{kWh} \times 3.6$

Conversion table

The table below lists common kilowatt-hour values and their equivalents in joules, kilojoules, and megajoules.

Examples

Example 1: One kilowatt-hour to joules

A space heater rated at 1 kW runs for exactly one hour, consuming 1 kWh. Converting this to joules:

$1 \text{ kWh} \times 3\,600\,000 = 3\,600\,000 \text{ J}$

Example 2: Two kilowatt-hours to joules

A household appliance uses 2 kWh over a cycle. The energy in joules is:

$2 \text{ kWh} \times 3\,600\,000 = 7\,200\,000 \text{ J}$

Example 3: Joules back to kilowatt-hours

A physics dataset reports 3,600,000 J of energy. Converting it back to the more familiar billing unit:

$\frac{3\,600\,000 \text{ J}}{3\,600\,000} = 1 \text{ kWh}$

Example 4: Kilowatt-hours to kilojoules

When working with kilojoules instead of plain joules, 1 kWh becomes:

$1 \text{ kWh} \times 3\,600 = 3\,600 \text{ kJ}$

Notes

• The factor 3,600,000 J per kWh is exact, not an approximation, because it follows directly from the definitions of the watt and the hour.
• A kilowatt-hour measures energy (kWh), while a kilowatt measures power (kW). Power tells you how fast energy is used; energy is power multiplied by time.
• Megajoules are often more convenient than raw joules for everyday electricity figures: 1 kWh is exactly 3.6 MJ.
• The calorie option in the converter uses the thermochemical calorie; expect roughly 859,845 cal per kWh.

Frequently asked questions

How many joules are in 1 kWh?

One kilowatt-hour equals exactly 3,600,000 joules, which is the same as 3.6 megajoules.

How do I convert joules to kilowatt-hours?

Divide the number of joules by 3,600,000. For example, 3,600,000 J divided by 3,600,000 gives 1 kWh.

Why is the conversion factor exactly 3,600,000?

Because 1 kW is 1,000 watts (joules per second) and one hour is 3,600 seconds, multiplying 1,000 by 3,600 yields 3,600,000 joules with no rounding.

What is the difference between a kilowatt-hour and a kilowatt?

A kilowatt (kW) is a unit of power, the rate of energy use, while a kilowatt-hour (kWh) is a unit of energy, the total amount used over time. If you also need to work with power units, try our kilowatts to watts converter.

How many kilojoules are in 1 kWh?

One kilowatt-hour equals 3,600 kilojoules. To go straight from kilojoules to joules, see our kilojoules to joules converter.

Is the kilowatt-hour an SI unit?

No. The joule is the SI unit of energy, but the kilowatt-hour is a non-SI unit accepted for use because it is so common in the electricity industry and on utility bills.