Energy Converter

100% Free

Convert energy between joules, calories, kilowatt-hours, BTU, electronvolts, and foot-pounds — instantly, in your browser.

11 Units

Instant

100% Client-Side

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Select input

Select output

Result

3,600,000 J

1 kWh = 3,600,000 J

All conversions from 1 kWh

Joule

3,600,000

Kilojoule

3,600

Megajoule

3.6

Calorie

860,420.65

cal

Kilocalorie

860.42065

kcal

Watt-hour

1,000

British Thermal Unit

3,412.1416

BTU

Therm (US)

0.034129563

thm

Electronvolt

2.2469e+25

Foot-pound

2,655,223.7

ft·lb

All values are normalised through the joule (J), the SI unit of energy. 1 kWh = 3,600,000 J, 1 kcal ≈ 4,184 J, and 1 BTU ≈ 1,055 J.

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How to Use

1 Enter the energy value you want to convert
2 Pick the unit you're converting from (e.g. kilowatt-hour)
3 Pick the unit you want the answer in (e.g. joule)
4 Read the converted value and the full conversion table instantly
5 Use the swap button to reverse the direction, or copy the result

Features

11 energy units across SI, calorie, electrical, imperial, and physics systems
Live conversion that updates as you type — no Calculate button needed
Full reference table showing the value in every unit at once
One-click swap between the from and to units
Scientific notation for very large or very small results
Runs entirely in your browser — nothing is uploaded

Why it Matters

Energy shows up in wildly different units depending on the field — joules in physics, calories in nutrition, kilowatt-hours on your electricity bill, BTU in heating and cooling. Converting between them by hand means remembering awkward constants and risking a slipped decimal. A single tool that normalises everything through the joule removes the guesswork.

★★★★★

Use Cases

Electricity Bills

Translate kWh on your meter into joules or BTU to compare appliances

Physics & Engineering

Switch between joules, electronvolts, and foot-pounds for problem sets

Nutrition & Fitness

Convert food calories and kilocalories to joules and back

Heating & Cooling

Work in BTU and therms when sizing HVAC and gas appliances

What this tool does

The Energy Converter turns any energy value from one unit into another — joules, calories, kilowatt-hours, BTU, electronvolts, foot-pounds, and more. Type a number, choose your units, and the converted value (plus a full reference table) appears instantly.

How it works

Every unit is defined by how many joules it represents, so the converter does a single multiply-then-divide: your value is converted to joules, then from joules into the target unit. Because the joule (the SI unit of energy) is the common pivot, all eleven units stay perfectly consistent. The logic is a pure function, so the same input always produces the same output.

Privacy

Everything runs locally in your browser. No values are uploaded, logged, or stored.

Frequently Asked Questions

How many joules are in one kilowatt-hour?

One kilowatt-hour equals exactly 3,600,000 joules (3.6 megajoules). A kilowatt-hour is one kilowatt of power sustained for one hour, and since a watt is a joule per second, that's 1,000 × 3,600 = 3.6 million joules. This is why the converter normalises every unit through the joule.

What's the difference between a calorie and a kilocalorie?

A calorie (cal) is about 4.184 joules. The 'calorie' on food labels is actually a kilocalorie (kcal) — 1,000 small calories, or about 4,184 joules. The converter lists both separately so you can pick the right one; nutrition figures almost always mean kilocalories.

Which units does the energy converter support?

Joule, kilojoule, and megajoule (SI); calorie and kilocalorie; watt-hour and kilowatt-hour (electrical); BTU and therm (imperial); plus the electronvolt and foot-pound. That covers everyday bills, nutrition, engineering, and physics in one place.

Why does the result sometimes show scientific notation?

Energy units span an enormous range — an electronvolt is about 1.6 × 10⁻¹⁹ joules, while a therm is over 100 million joules. When a result is extremely large or extremely small, the converter switches to scientific notation so the value stays readable and precise.

Is my data sent anywhere?

No. The conversion runs entirely in your browser using fixed constants. Nothing you type is uploaded, logged, or stored — refreshing the page clears everything.

📖

Want to understand the conversions?

Browse all guides →

Energy Units Explained

energy units

Energy Units Explained: Joules, Calories, kWh & BTU

A plain-English guide to energy units — what a joule, calorie, kilowatt-hour, and BTU actually measure, how they relate, and how to convert between them without slipping a decimal.

23 Jun 2026

5 min read

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