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Energy Conversion
Tool Description
Energy Conversion is an online energy unit conversion tool that supports mutual conversion between joule (J), kilojoule (kJ), calorie (cal), kilocalorie (kcal), watt-hour (Wh), kilowatt-hour (kWh), electronvolt (eV), British thermal unit (BTU), and foot-pound (ft·lbf). Simply enter any value and unit to instantly view the corresponding results in all other units — ideal for physics learning, nutrition calculation, electricity consumption, engineering mechanics, and more.
How to Use
- Enter a value
Enter the value to convert in the input box. Both integers and decimals are supported, e.g.
1000,4.184 - Select source unit
Choose the energy unit of the current value from the dropdown (J/
kJ/ cal/ kcal/ Wh/ kWh/ eV/ BTU/ ft·lbf) - View results
Click the "Convert" button or press Enter — the results area below will display the corresponding values in all units, with a copy button beside each result for convenience
Use Cases
- Physics Learning: Quickly switch between joules, electronvolts, and other units in work and energy calculations; convert between calories and joules in thermodynamics
- Nutrition & Health: Quickly convert energy values (kcal/kJ) on food packaging; understand daily caloric intake; convert exercise calories to joules
- Electricity & Energy: Convert household appliance power consumption (kWh) to joules; understand the energy corresponding to electricity bills; convert between watt-hours and joules in solar power and battery capacity scenarios
Core Advantages
- Free & No Registration
The online energy unit converter is completely free. Just open the page and use it — no account registration or software installation required
- Local & Private
All conversions run locally in your browser. Your input data is never uploaded to any server, fully protecting your privacy
- Instant Calculation
Results are calculated instantly as you type, with no waiting — all unit results are shown at a glance
- Comprehensive Units
Supports 9 energy units including joules, calories, watt-hours and electronvolts, covering physics, nutrition and electricity
- High Precision
Uses exact mathematical computation; electronvolt uses the SI 2019 exact value (1 eV = 1.602176634×10⁻¹⁹ J) and supports decimals and extreme values
- Cross-platform
Works smoothly on desktop, mobile and tablet. The page is responsive and lets you convert units anytime, anywhere
Energy Unit Conversion Relationships
The following shows the conversion relationships between energy units, with joule (J) as the base unit:
| Unit Name | Abbr | Conversion | Equivalent Joules |
|---|---|---|---|
| Joule | J | 1 J = 1 N·m | 1 |
| Kilojoule | kJ | 1 kJ = 10³ J | 1,000 |
| Calorie | cal | 1 cal = 4.184 J | 4.184 |
| Kilocalorie | kcal | 1 kcal = 4,184 J | 4,184 |
| Watt-hour | Wh | 1 Wh = 3,600 J | 3,600 |
| Kilowatt-hour | kWh | 1 kWh = 3.6×10⁶ J | 3,600,000 |
| Electronvolt | eV | 1 eV ≈ 1.602×10⁻¹⁹ J | 1.602176634×10⁻¹⁹ |
| British Thermal Unit | BTU | 1 BTU ≈ 1,055.06 J | 1,055.06 |
| Foot-pound | ft·lbf | 1 ft·lbf ≈ 1.35582 J | 1.35582 |
Common Energy Units by Field
Different industries and disciplines use different energy units. Understanding their applications helps you better use the conversion tool.
The table below lists the most common application fields and typical examples for each energy unit:
| Energy Unit | Application Field | Typical Example |
|---|---|---|
| J, kJ | Physics, Engineering | Kinetic energy of moving objects, spring potential energy |
| cal, kcal | Nutrition, Food | Food label calories, daily intake |
| Wh, kWh | Electricity, Appliances | Electricity bills, battery capacity |
| eV | Particle Physics, Semiconductors | Photon energy, band gap |
| BTU | HVAC, Refrigeration | AC cooling capacity, boiler power |
| ft·lbf | Mechanical Engineering | Torque work, engine output |
FAQ
1 calorie (cal) = 4.184 joules (J). This is the international standard definition of the thermochemical calorie. The "large calorie" commonly referred to in daily life is the kilocalorie (kcal): 1 kcal = 1,000 cal = 4,184 J. Calories on food labels are typically expressed in kcal, sometimes also labeled as kJ.
1 kilowatt-hour (kWh) = 3,600,000 joules (J), i.e. 3.6 × 10⁶ J. Calculation: 1 kWh = 1,000 W × 3,600 s = 3,600,000 J. For example, a 1,000W air conditioner running for 1 hour consumes 1 kWh of electricity, which equals 3.6 MJ of energy.
An electronvolt (eV) is an extremely small unit of energy, 1 eV ≈ 1.602176634 × 10⁻¹⁹ J, defined as the kinetic energy gained by a single electron accelerated through a potential difference of 1 volt. It is primarily used in microscopic physics: atomic energy level transitions (typically eV~keV range), semiconductor band gaps (~1 eV), and particle physics (commonly MeV, GeV). Because its magnitude matches atomic-scale energies, it is much more intuitive and convenient than joules.
BTU (British Thermal Unit) is a commonly used energy unit in the US and UK, 1 BTU ≈ 1,055.06 J ≈ 0.252 kcal, defined as the amount of heat required to raise the temperature of 1 pound of water by 1°F. It is primarily used in HVAC (Heating, Ventilation, and Air Conditioning), such as air conditioner cooling capacity (BTU/h) and boiler heating power. For example, a "12,000 BTU air conditioner" is roughly equivalent to 1.5 tons of cooling capacity.
No. All conversion calculations run entirely in your browser using pure JavaScript math. Your input data never leaves your device.
This tool uses JavaScript double-precision floating-point numbers (64-bit IEEE 754) for calculations, which is sufficiently accurate for the vast majority of everyday scenarios. Electronvolt conversion uses the latest SI 2019 exact value (1 eV = 1.602176634×10⁻¹⁹ J). Decimal portions are capped at 6 significant decimal places, and excessively long decimals are automatically truncated. For extremely large or small values, there may be minor errors due to floating-point precision limitations, but this has virtually no practical impact.
9 units in total. Including joule (J), kilojoule (kJ), calorie (cal), kilocalorie (kcal), watt-hour (Wh), kilowatt-hour (kWh), electronvolt (eV), BTU and foot-pound (ft·lbf). Enter any unit and convert to all the others at once.
1 kilocalorie = 1,000 calories. The "large calorie" on food labels is the kilocalorie, where 1 kcal = 4,184 J, while the small cal is only 4.184 J. The tool applies the 1,000× relationship automatically.
Both are electrical energy units. 1 kWh = 1,000 Wh, commonly called "one degree of electricity" = 3.6 MJ. Wh is often used for battery capacity (e.g. a 20,000 mAh power bank ≈ 74 Wh), while kWh is used for electricity metering. The tool converts freely between them and joules.
Click the copy button next to each result. A one-click copy button is provided beside every unit result — click it and the value goes to your clipboard, ready to paste into documents, spreadsheets or chats.
Yes. The page is responsive and works on phones, tablets and desktop browsers. Input and result-copying work on mobile too.
Completely free and registration-free. Just open the page to use it directly — no login required and no fees charged.
Content last updated：2026-07-16
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