Energy Converter

Energy is measured in units that evolved independently for different domains: joules and kilojoules for physics and chemistry, kilowatt-hours for electricity billing, calories and kilocalories for nutrition, BTUs for US heating systems. A food calorie (kcal) is exactly 4.184 kJ; a kilowatt-hour is 3.6 MJ — relationships that matter when comparing the energy content of food, fuel, and electricity. This converter covers all common energy units, making it straightforward to compare a meal's calorific value with the power draw of an appliance.

Energy Conversion Guide

Understanding Energy Measurements

The joule (J) is the SI unit of energy, defined as one newton-metre (N·m) or one watt-second (W·s). The kilowatt-hour (kWh = 3.6 MJ exactly) is the practical unit for electrical energy billing. The thermochemical calorie (cal = 4.184 J exactly) is the basis for the food calorie (kcal = 4,184 J). The British thermal unit (BTU = 1,055.06 J) remains in use in US heating, ventilation, and air conditioning. The electron-volt (eV = 1.602 176 634 × 10⁻¹⁹ J) is standard in atomic and particle physics.

All conversions in this category are computed relative to a single base unit — Joule — using factors sourced from NIST Special Publication 811 and the BIPM SI Brochure. Anchoring every conversion to one reference unit guarantees mathematical consistency: converting from A → B → C always yields the same result as converting directly from A → C.

Common Energy Units

Among the 14 supported units, the most frequently used include Joule, Kilojoule, Megajoule, Gigajoule, Calorie. These appear across household tasks, professional environments, and academic study.

Many units carry aliases and regional abbreviations that appear in product specs, recipes, and technical documents. We index common synonyms so searches for alternate spellings still reach the right converter — for example, Joule (J, also written as joule or joules), or Kilojoule (kJ, also written as kilojoule or kilojoules), or Megajoule (MJ, also written as megajoule or megajoules).

How to Convert Energy Accurately

All energy conversions within the SI family are purely multiplicative — you multiply the source value by a fixed conversion factor derived from the ratio of the two unit definitions. Imperial-to-metric conversions use the exact defined equivalences (e.g., 1 inch = 25.4 mm exactly) rather than approximations.

When precision matters — machining tolerances, pharmaceutical compounding, scientific reporting — avoid intermediate rounding. Each converter page shows the full unrounded factor so you can carry maximum precision through multi-step calculations and only round the final result.

Real-World Applications of Energy Units

In daily practice, choosing the right energy unit saves time and prevents costly errors. Commercial shipping, construction, and scientific research all depend on correct unit handling to maintain safety, compliance, and reproducibility across borders and disciplines.

Consumer products, regulations, and international standards often specify values in different unit systems — a drug dosage in micrograms, a fuel efficiency in L/100 km, a tyre pressure in PSI. Each domain has a dominant unit, and cross-domain work requires reliable conversion. This converter is built for exactly those situations: results traceable to internationally defined constants, displayed with full precision.

Available Energy Units

Joule (J)
Also: joule, joules
Kilojoule (kJ)
Also: kilojoule, kilojoules
Megajoule (MJ)
Also: megajoule, megajoules
Gigajoule (GJ)
Also: gigajoule, gigajoules
Calorie (cal)
Also: calorie, calories
Kilocalorie (kcal)
Also: kilocalorie, kilocalories
Watt-hour (Wh)
Also: watt hour, watt-hour
Kilowatt-hour (kWh)
Also: kilowatt hour, kilowatt-hour
Megawatt-hour (MWh)
Also: megawatt hour, megawatt-hour
British Thermal Unit (BTU)
Also: btu, british thermal unit
Therm (therm)
Also: therms
Foot-pound (ft-lb)
Also: foot-pound, foot pound
Electronvolt (eV)
Also: electronvolt, electron volt
Erg (erg)
Also: erg, ergs

Popular Energy Converters

Start with these commonly useful converter pages, then use each page's related links for reverse and nearby conversions.

Joule to Kilojoule J to kJ Joule to Calorie J to cal Joule to Kilocalorie J to kcal Joule to British Thermal Unit J to BTU Joule to Therm J to therm Joule to Foot-pound J to ft-lb Kilojoule to Joule kJ to J Kilojoule to Megajoule kJ to MJ Kilojoule to Kilocalorie kJ to kcal Kilojoule to British Thermal Unit kJ to BTU

All Energy Converters

Each link opens a dedicated converter page with a formula, examples, table, manual steps, FAQ, and related converters.

Joule to Kilojoule J ⇄ kJ Joule to Calorie J ⇄ cal Joule to Kilocalorie J ⇄ kcal Joule to British Thermal Unit J ⇄ BTU Joule to Therm J ⇄ therm Joule to Foot-pound J ⇄ ft-lb Kilojoule to Joule kJ ⇄ J Kilojoule to Megajoule kJ ⇄ MJ Kilojoule to Kilocalorie kJ ⇄ kcal Kilojoule to British Thermal Unit kJ ⇄ BTU Kilojoule to Therm kJ ⇄ therm Kilojoule to Foot-pound kJ ⇄ ft-lb Megajoule to Kilojoule MJ ⇄ kJ Megajoule to Gigajoule MJ ⇄ GJ Megajoule to Kilowatt-hour MJ ⇄ kWh Megajoule to British Thermal Unit MJ ⇄ BTU Megajoule to Therm MJ ⇄ therm Megajoule to Foot-pound MJ ⇄ ft-lb Gigajoule to Megajoule GJ ⇄ MJ Gigajoule to British Thermal Unit GJ ⇄ BTU Gigajoule to Therm GJ ⇄ therm Gigajoule to Foot-pound GJ ⇄ ft-lb Calorie to Joule cal ⇄ J Calorie to Kilocalorie cal ⇄ kcal Calorie to British Thermal Unit cal ⇄ BTU Calorie to Therm cal ⇄ therm Calorie to Foot-pound cal ⇄ ft-lb Kilocalorie to Joule kcal ⇄ J Kilocalorie to Kilojoule kcal ⇄ kJ Kilocalorie to Calorie kcal ⇄ cal Kilocalorie to British Thermal Unit kcal ⇄ BTU Kilocalorie to Therm kcal ⇄ therm Kilocalorie to Foot-pound kcal ⇄ ft-lb Watt-hour to Kilowatt-hour Wh ⇄ kWh Watt-hour to British Thermal Unit Wh ⇄ BTU Watt-hour to Therm Wh ⇄ therm Watt-hour to Foot-pound Wh ⇄ ft-lb Kilowatt-hour to Megajoule kWh ⇄ MJ Kilowatt-hour to Watt-hour kWh ⇄ Wh Kilowatt-hour to Megawatt-hour kWh ⇄ MWh Kilowatt-hour to British Thermal Unit kWh ⇄ BTU Kilowatt-hour to Therm kWh ⇄ therm Kilowatt-hour to Foot-pound kWh ⇄ ft-lb Megawatt-hour to Kilowatt-hour MWh ⇄ kWh Megawatt-hour to British Thermal Unit MWh ⇄ BTU Megawatt-hour to Therm MWh ⇄ therm Megawatt-hour to Foot-pound MWh ⇄ ft-lb British Thermal Unit to Joule BTU ⇄ J British Thermal Unit to Kilojoule BTU ⇄ kJ British Thermal Unit to Megajoule BTU ⇄ MJ British Thermal Unit to Gigajoule BTU ⇄ GJ British Thermal Unit to Calorie BTU ⇄ cal British Thermal Unit to Kilocalorie BTU ⇄ kcal British Thermal Unit to Watt-hour BTU ⇄ Wh British Thermal Unit to Kilowatt-hour BTU ⇄ kWh British Thermal Unit to Megawatt-hour BTU ⇄ MWh Therm to Joule therm ⇄ J Therm to Kilojoule therm ⇄ kJ Therm to Megajoule therm ⇄ MJ Therm to Gigajoule therm ⇄ GJ Therm to Calorie therm ⇄ cal Therm to Kilocalorie therm ⇄ kcal Therm to Watt-hour therm ⇄ Wh Therm to Kilowatt-hour therm ⇄ kWh Therm to Megawatt-hour therm ⇄ MWh Foot-pound to Joule ft-lb ⇄ J Foot-pound to Kilojoule ft-lb ⇄ kJ Foot-pound to Megajoule ft-lb ⇄ MJ Foot-pound to Gigajoule ft-lb ⇄ GJ Foot-pound to Calorie ft-lb ⇄ cal Foot-pound to Kilocalorie ft-lb ⇄ kcal Foot-pound to Watt-hour ft-lb ⇄ Wh Foot-pound to Kilowatt-hour ft-lb ⇄ kWh Foot-pound to Megawatt-hour ft-lb ⇄ MWh

Energy Converter FAQ

How many energy units are supported?

This category supports 14 units: Joule, Kilojoule, Megajoule, Gigajoule, Calorie, Kilocalorie, Watt-hour, Kilowatt-hour, Megawatt-hour, British Thermal Unit, Therm, Foot-pound, Electronvolt, Erg.

How do I convert energy units?

Choose a source and target unit, enter a value, and multiply through the J base-unit factors shown on the dedicated converter page.

Which energy conversion should I start with?

Joule to Kilojoule is a useful starting point, and the related links on that page connect to reverse and nearby conversions.

Are energy conversions available without JavaScript?

Yes. Category descriptions, unit lists, converter links, FAQs, and structured data are rendered in the initial HTML source.

Are energy converter URLs canonical?

Yes. Each converter page uses one trailing-slash canonical URL and the sitemap lists those same canonical URLs.