AnyTool
Your files never leave your device. All processing happens locally in your browser.

How do I convert energy between joules, calories, kWh and BTU?

Type a value into AnyTool Energy Converter and pick the units. It instantly converts both ways between joules, kilojoules, megajoules, calories, kilocalories (food Calories), watt-hours, kilowatt-hours, megawatt-hours, BTU, therms, foot-pounds, electronvolts and ergs, and shows the value in every unit at once in a copyable table. Everything is calculated in your browser, so nothing is uploaded.

  • Live two-way conversion — type in either field and the other updates
  • Joule, kJ, MJ, calorie, kcal/food Calorie, Wh, kWh, MWh, BTU, therm, ft·lbf, eV and erg
  • See the value in every unit at once, each row copyable
  • Exact, internationally-defined factors through a joule base
  • 100% in your browser — no upload, no signup, works offline

What is

Energy Conversion

Energy conversion changes an amount of energy from one unit to another — for example kilowatt-hours to joules. The joule is the SI unit (one newton-metre), and every other energy unit is a fixed multiple of it, so conversion is a single multiply and divide through a joule base. One kilowatt-hour is exactly 3,600,000 joules and one calorie (thermochemical) is exactly 4.184 joules.

Converters

Related terms

JouleKilowatt-hourCalorie vs kilocalorieBTUElectronvolt

Frequently Asked Questions

A kilowatt-hour is exactly 3,600,000 joules — one kilowatt sustained for one hour.

One kilowatt-hour equals exactly 3,600,000 joules (3.6 megajoules), because a watt is one joule per second and an hour is 3600 seconds: 1000 W × 3600 s = 3,600,000 J. The kilowatt-hour is the unit your electricity bill is measured in, while the joule is the underlying SI unit.

The food "Calorie" is actually a kilocalorie — 1000 small calories, or 4184 joules.

A small calorie (cal) is about 4.184 joules. The "Calorie" on food labels, written with a capital C, is really a kilocalorie (kcal) = 1000 small calories = 4184 joules. So a 200-Calorie snack contains 200 kcal, or roughly 836,800 joules. AnyTool lists both the small calorie and the kilocalorie separately so you never mix them up.

No. Every calculation runs in your browser, so nothing is sent to a server and it works offline.

AnyTool Energy Converter computes every result locally in JavaScript using exact conversion factors through a joule base. No value is uploaded, there is no tracking, and the page keeps working offline after the first load.

One BTU (International Table) is exactly 1055.05585262 joules.

One British thermal unit (International Table) equals exactly 1055.05585262 joules. It is widely used for heating, cooling and gas appliances. A therm, the unit on US gas bills, is exactly 100,000 BTU = 105,505,585.262 joules. AnyTool converts BTU and therms alongside joules, calories and kilowatt-hours.

Detailed Explanation

Methodology

How the Energy Converter Works

AnyTool Energy Converter performs every calculation in the browser. Each unit declares a single linear factor relative to a shared joule base — the exact number of joules in one of that unit — so any unit converts to any other through joules without an N-by-N table. The factors are the internationally-agreed definitions: a kilowatt-hour is exactly 3,600,000 J, a watt-hour 3600 J, a thermochemical calorie 4.184 J, a food Calorie (kilocalorie) 4184 J, an International Table BTU 1055.05585262 J, a therm 100,000 of those BTU, a foot-pound 1.3558179483314 J, an electronvolt 1.602176634×10⁻¹⁹ J and an erg 1×10⁻⁷ J. A value is multiplied to joules and then divided into the target unit.

  • Thirteen units spanning SI, electrical, thermal and physics scales
  • The joule is the shared base; each unit is one exact factor
  • Conversion is value to base to value, so any unit maps to any other
  • Editing either field converts both directions live
  • All arithmetic is client-side JavaScript — no server round-trip
How It Works

Calories, Kilocalories and Other Confusable Units

The calorie is the most misread energy unit, so AnyTool lists two: the small (thermochemical) calorie of exactly 4.184 J and the kilocalorie of 4184 J, which is the "food Calorie" printed with a capital C on nutrition labels. A 250-Calorie snack is therefore 250 kcal, not 250 cal. The converter also separates the watt-hour family (Wh, kWh, MWh) used for electricity from the BTU and therm used for heating and gas, and includes the electronvolt and erg for physics. A single input is shown in every unit at once in a copyable table, with adjustable precision and automatic scientific notation for very large or very small magnitudes such as electronvolts.

  • Small calorie (4.184 J) and food Calorie / kcal (4184 J) listed separately
  • Watt-hour, kilowatt-hour and megawatt-hour for electricity
  • BTU (International Table) and therm for heating and gas bills
  • Electronvolt and erg for atomic, particle and CGS physics
  • Convert-to-all table with adjustable precision and scientific notation
Privacy & Security

Privacy and Offline Use

Because all conversion runs in the browser, no value is sent to a server, there is no account or tracking, and the page works offline after first load. The converter is built on a shared, unit-tested conversion engine that other AnyTool unit converters reuse, so behaviour is consistent across the site.

Energy conversion: in-browser (AnyTool) vs typical online converters
CapabilityAnyToolTypical online converters
ProcessingRuns in your browserOften server-side
Units13: J, kJ, MJ, cal, kcal, Wh, kWh, MWh, BTU, therm, ft·lbf, eV, ergOften a handful (J, cal, kWh, BTU)
Calorie claritySmall calorie and food Calorie (kcal) listed separatelyOften ambiguous "calorie"
Two-way inputEdit either field, both updateUsually one-direction with a button
All units at onceYes, copyable tableOften one target at a time
Precision controlAdjustable decimalsFrequently fixed
Works offlineYes (PWA)No
Cost / signupFree, no signupOften ad-heavy or gated

AnyTool converts every unit locally through a joule base and uploads nothing.