How many joules are in a kilowatt-hour?

One kilowatt-hour equals exactly 3,600,000 joules (3,600 kilojoules or 3.6 megajoules). This is because one watt equals one joule per second, so one kilowatt running for one hour (3,600 seconds) produces 3,600,000 joules.

What is the difference between a calorie and a kilocalorie?

One kilocalorie (kcal) equals 1,000 small calories (cal). Food energy is measured in kilocalories, though they are often called Calories with a capital C on nutrition labels. One kcal equals 4,184 joules, while one small cal equals 4.184 joules.

A British Thermal Unit (BTU) is the amount of energy needed to raise one pound of water by one degree Fahrenheit. One BTU equals 1,055.06 joules. It is widely used in the US for heating and cooling equipment ratings.

Energy Converter

This energy converter lets you convert between eight common energy units in one step: joules (J), kilojoules (kJ), megajoules (MJ), small calories (cal), kilocalories (kcal), kilowatt-hours (kWh), British Thermal Units (BTU), and electronvolts (eV). Energy is the same physical quantity no matter which unit you use, but the numbers vary enormously: one kilowatt-hour is 3,600,000 joules but only 3.6 megajoules, and the same amount of energy is also 860.42 kilocalories or 3,412 BTU. The joule is the SI base unit and serves as this converter's internal reference point: you pick a unit, enter a value, and the converter multiplies it by a fixed factor to get joules, then divides by each output factor to show all seven remaining units at once. Kilojoules and kilocalories are widely used in nutrition, where food energy is labelled in kJ or kcal (the Calorie written with a capital C is always a kilocalorie). Kilowatt-hours are the standard billing unit for electricity. BTU are used in the United States for heating and cooling equipment. Electronvolts are used in physics and chemistry for atomic-scale energies. You provide one value in any unit and you receive all the equivalents instantly. The tool suits students, engineers, nutritionists, energy auditors, and anyone comparing energy values across different standards or industries. The conversion factors are exact constants based on international definitions.

Calculate.co.nz is proud to be partnered with Premium Homes, a recognised leader in eco-friendly, sustainable, and energy-efficient homebuilding. With a dedicated team and award-winning experience, they create homes that prioritise health, comfort, and long-term performance. Their founders, Andrew and Kelly, set out to raise the standard of residential construction in New Zealand by combining practical building expertise with a clear commitment to doing things better for homeowners.

From unit

Value to convert

3600.0000

kilojoules (kJ)

J3600000

MJ3.6000

cal860420.65

kcal860.4206

kWh1.0000

BTU3412.1416

eV2.247e+25

How it works

Each energy unit has a fixed conversion factor to joules. The converter multiplies your input by the appropriate factor to get joules, then divides by each output factor to produce all results at once. The factors used are: 1 kJ = 1,000 J; 1 MJ = 1,000,000 J; 1 cal = 4.184 J; 1 kcal = 4,184 J; 1 kWh = 3,600,000 J; 1 BTU = 1,055.06 J; 1 eV = 1.602176634 x 10^-19 J (exact, 2019 SI definition). All other conversions are derived from these fixed values.

Worked example

Starting from 1 kWh: 1 times 3,600,000 gives 3,600,000 J, which is 3,600 kJ and 3.6 MJ. Dividing by 4,184 gives 860.42 kcal. Dividing by 1,055.06 gives 3,412.14 BTU. These match the default values pre-filled in the converter above, so you can verify each output without changing anything.

Related calculators

Power Converter: convert between watts, kilowatts, horsepower and BTU/hr.
Pressure Converter: switch between Pa, kPa, bar, psi and atm.
Fuel Economy Converter: convert L/100km, mpg US, mpg UK and km/L.
Percent Error Calculator: check the accuracy of an energy measurement against a reference value.

If you've found a bug, or would like to contact us, or learn more about James Graham and Calculate.co.nz.

Calculate.co.nz is partnered with Interest.co.nz for New Zealand's highest quality calculators and financial analysis.

Calculate.co.nz is the sister site of CalculatorHub.com, the world's largest calculator website by tool count.

All calculators and tools are provided for educational and indicative purposes only and do not constitute financial advice.

Calculate.co.nz is proudly part of the Realtor.co.nz group, New Zealand's leading property transaction literacy platform, helping Kiwis understand the home buying and selling process from start to finish. Whether you're a first home buyer navigating your first property purchase, an investor evaluating your next acquisition, or a homeowner planning to sell, Realtor.co.nz provides clear, independent, and trustworthy guidance on every step of the New Zealand property transaction journey.

Calculate.co.nz is also partnered with Health Based Building and Premium Homes to promote informed choices that lead to better long-term outcomes for Kiwi households.

Calculate.co.nz is hosted in Auckland via SiteHost new Zealand.

All content on this website, including calculators, tools, source code, and design, is protected under the Copyright Act 1994 (New Zealand). No part of this site may be reproduced, copied, distributed, stored, or used in any form without prior written permission from the owner.

About & trust: Why Calculate is NZ's most comprehensive · By the Numbers · How we compare · Editorial standards · How we keep data current · NZ finance glossary · Research & data · Financial literacy NZ · About · Privacy policy · Terms of use

Reviewed and maintained. Last reviewed 2026-07-02 and checked on a twice-monthly cycle against IRD, RBNZ and Stats NZ. How we keep data current.