Energy converter
Convert joules, kilojoules, watt-hours, kilowatt-hours and explicitly defined calories.
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How it works
Convert energy or a signed energy change between joules, watt-hours, explicitly named calorie definitions and mechanical work units. Kilowatt-hours are energy, not power. Thermochemical and International Table calories are offered separately to avoid concealing their different definitions.
A few things to know
Unit conversion only, not electricity cost, metabolic advice or appliance consumption prediction. No energy transfer efficiency is modeled. Signed values preserve an energy-change convention rather than implying negative fuel content. Calorie and BTU definitions are explicitly selected; temperature-specific variants are excluded. Display uses up to 12 significant digits; this is not arbitrary-precision arithmetic or a measurement calibration. Numeric magnitude is bounded to 1e100, with nonzero inputs at least 1e-100.
When to use this tool
Joules, watt-hours and calories can describe energy, but watts describe a rate of energy transfer. This converter keeps those quantities distinct and translates a numeric energy value among SI multiples, watt-hours, mechanical work units and explicitly named calorie or BTU definitions. Thermochemical and International Table calories have different factors and remain separate choices. Signed values can represent an energy change under your own convention. The result does not estimate electricity charges, device efficiency or the energy content of an item you have not measured.
- Express an electricity energy amount in kilowatt-hours as megajoules.
- Compare a thermochemical kilocalorie figure with a kilojoule value.
- Translate mechanical work in foot-pounds-force into joules for a separate documented calculation.
How to use energy converter
Enter a known energy quantity
Put the numeric amount in Value. Positive, zero and signed energy-change values are accepted; enter energy rather than a power rating.
Choose the definition precisely
Set From unit, including the calorie or BTU variant where relevant. Thermochemical and International Table labels use different factors.
Read an energy equivalent
Choose To unit and calculate. Check Converted value or the equivalent-energy table, then download the CSV if it supports your next calculation.
One kilowatt-hour in megajoules
Inputs
Value 1; From unit Kilowatt-hours (kWh); To unit Megajoules (MJ).
Result
Converted value is 3.6 megajoules. The table also shows 3,600,000 joules and 1,000 watt-hours.
What it means
A kilowatt-hour represents one kilowatt of power sustained for one hour. Multiplying 1,000 joules per second by 3,600 seconds gives 3.6 million joules. The conversion supplies no electricity price or efficiency adjustment.
Common mistakes to avoid
Treating kW as kWh
Kilowatts measure power. Kilowatt-hours measure energy accumulated over time. A power rating alone is not a value this tool can convert.
Ignoring calorie variants
Thermochemical and International Table calories differ. Select the definition documented by your source rather than assuming the word calorie fixes it.
Inferring useful output energy
A unit change does not account for energy lost in a process. Efficiency, losses and operating behavior are separate calculations.
Frequently asked questions
Definitions, edge cases, and practical next steps for this tool. Search all tool FAQs ↗
How is an energy quantity converted?
The source value is multiplied by its joule factor and divided by the target unit’s joule factor. Each table row represents the same energy amount. The calculation does not introduce a time period, process efficiency or tariff.
What is the difference between watts and watt-hours?
A watt is a joule per second, so it measures power. A watt-hour is the energy transferred by one watt over an hour and equals 3,600 joules. Converting a power rating to energy also requires its operating duration.
How many joules are in a kilowatt-hour?
One kilowatt-hour equals 3,600,000 joules, or 3.6 megajoules. The factor combines 1,000 watts per kilowatt and 3,600 seconds per hour. It expresses energy and should not be abbreviated as a kilowatt power value.
Why are two calorie definitions listed?
A thermochemical calorie is 4.184 joules, while an International Table calorie is 4.1868 joules. The source’s definition matters for a precise conversion. Temperature-specific calorie variants are not included, and the converter does not guess which convention an unlabeled source intended.
Does a food Calorie mean one small calorie?
Food-energy wording commonly refers to a kilocalorie, which is 1,000 small calories under the chosen definition. This tool labels kilocalories explicitly and lets you choose the definition. It does not inspect nutrition labels or provide dietary advice.
Which BTU definition does the converter use?
The listed option is the International Table BTU, with a factor of 1,055.05585262 joules. Other BTU conventions are excluded. Check the definition in an engineering source before selecting it, especially when reconciling values quoted with high precision.
Why can I enter negative energy?
A signed quantity can describe an energy change relative to a convention, such as energy leaving a system. The converter preserves the sign. It does not imply negative fuel content or choose the sign convention for heat, work or another physical process.
Can this estimate an electricity bill or appliance consumption?
It converts energy already known. Estimating consumption requires actual power over time, and estimating a bill also requires tariffs and any relevant charges. Neither operating behavior nor prices are inputs here, so the result alone cannot supply those estimates.
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Sources and method
Use the references below to check definitions and platform guidance. The model’s scope and limits are explained above. Read our editorial standards.