Why is the number so large?

The joule is a small unit — lifting an apple one metre takes about one joule. Household energy needs millions of them, which is why kWh exists.

How do I convert MJ or GJ to kWh?

Divide MJ by 3.6, or GJ by 0.0036. One gigajoule is 277.8 kWh.

Is this conversion exact?

Yes. Both units are SI-derived and the relationship involves no measured constants.

Joules to kWh Converter | J to Kilowatt-hours Calculator

Conversion Formula

kWh = J ÷ 3,600,000

One kilowatt-hour contains 3.6 million joules. Divide joules by 3,600,000 to express any SI energy figure in billing units.

Complete Guide to Joules to Kilowatt-hours Conversion

What is a Joules?

The joule (J) is the SI unit of energy, defined as one newton-metre of work. It is the base against which every other energy unit is defined, and it is the unit used in scientific literature and international standards.

What is a Kilowatt-hours?

A kilowatt-hour (kWh) is a practical commercial unit equal to one kilowatt sustained for one hour — the unit on electricity meters, EV batteries and solar quotes.

How the Conversion Works

Because a watt is a joule per second, a kilowatt delivers 1,000 joules every second. Over one hour — 3,600 seconds — that is 3,600,000 joules. The relationship is definitional and therefore exact in both directions.

Why This Conversion Matters

Scientific and commercial energy worlds use different units for the same physical quantity. Being able to move between them is what lets an engineer compare a datasheet in joules with a utility bill in kilowatt-hours, or check whether a stated energy density is plausible.

Scientific Context

Since the 2019 SI redefinition, the joule is fixed through the Planck constant, the metre and the second. The kilowatt-hour is a legacy commercial unit accepted for use alongside SI but not part of it.

Step-by-Step Conversion Guide

Follow these steps to convert joules to kilowatt-hours manually:

Start with your value in joules

Example: You want to convert 1000000 J

Apply the conversion formula

Use the formula: kWh = J ÷ 3,600,000

Calculate the result

1000000 J = 0.2778 kWh

✓

Verify your answer

Use our calculator above to double-check your manual calculation.

Quick Mental Math Tip

One kilowatt-hour contains 3.6 million joules. Divide joules by 3,600,000 to express any SI energy figure in billing units.

Common Conversions

Joules to Kilowatt-hours conversion table
Joules (J)	Kilowatt-hours (kWh)	Kilowatt-hours → Joules
1000	0.0003	1000 kWh = 3600000000 J
100000	0.0278	100000 kWh = 360000000000 J
1000000	0.2778	1000000 kWh = 3600000000000 J
3600000	1	3600000 kWh = 12960000000000 J
10000000	2.7778	10000000 kWh = 36000000000000 J
36000000	10	36000000 kWh = 129600000000000 J
100000000	27.7778	100000000 kWh = 360000000000000 J

When You'll Need This Conversion

Physics and engineering problems

Convert real electricity data into SI units for calculation.

Reading technical standards

IEC and ISO documents express energy in joules; equipment is marketed in kWh.

Thermal storage design

Heat storage capacity is often derived in joules then reported in kWh.

Understanding energy density claims

Battery and fuel energy densities are quoted in MJ/kg or Wh/kg — the same quantity in different clothes.

Pro Tips for Accurate Conversions

Work in MJ, not J

3.6 MJ per kWh is far easier to handle than 3,600,000 J.

Watts × seconds = joules

The shortest route from a power rating to an energy figure.

Check magnitudes

A household day is tens of megajoules. If you land in kilojoules, a prefix went missing.

Common Mistakes to Avoid

Dropping a prefix between J, kJ and MJ

Each step is a factor of 1,000 and errors compound quickly.

Write the exponent explicitly in calculations: 3.6 × 10⁶ J per kWh.

Confusing joules with watts

Watts are joules per second — a rate, not a quantity.

Multiply watts by time in seconds to obtain joules.

Using 3.6 million where 3.6 belongs

The factor is 3.6 for MJ and 3,600,000 for J.

Confirm which prefix your source uses before converting.

History & Background

The joule was adopted as the single SI unit of energy in 1948, unifying mechanical, thermal and electrical energy that had previously each had their own units.