Free Online Energy Converter — Convert Any Energy Unit Instantly
Energy unit conversion made simple. Convert between joules, calories, kilowatt-hours, BTU, electronvolts, ergs, and 15+ energy units with precise, real-time results — completely free and private.
Convert Your Energy Value
How to Use This Energy Converter
Enter Your Energy Value
Type the numeric energy value you want to convert into the input field. Use decimal points for precise values.
Select the Source Unit
Choose the energy unit you are converting from using the "From Unit" dropdown menu. Options include joules, calories, kWh, BTU, and more.
Select the Target Unit
Choose the energy unit you want to convert to using the "To Unit" dropdown. You can also use the swap button to reverse the direction.
Click Convert Energy
Press the Convert Energy button or hit Enter to perform the conversion. The result appears instantly below.
Copy or Review All Conversions
Copy the result using the Copy Result button, or expand the full conversion table to see the value expressed in all 15 supported units simultaneously.
Key Features of Energy Converter
100% Free Energy Conversion
Convert between any energy units without limits, fees, or account registration. Unlimited conversions, always.
15+ Supported Energy Units
Covers SI units (joule, kilojoule), thermal units (calorie, BTU), electrical units (Wh, kWh), and physics units (eV, erg).
Instant Real-Time Results
Conversions complete in under 1 millisecond with high-precision arithmetic and automatic scientific notation for extreme values.
Complete Privacy Protection
All calculations run locally in your browser using JavaScript. No server requests, no data collection, no tracking of any kind.
No Registration Required
Start converting immediately. No signup forms, no email verification, no premium upgrades — just open and use.
Mobile-Friendly Responsive Design
Optimized layout for smartphones, tablets, and desktops with touch-friendly controls and adaptive grid sizing.
How Energy Conversion Works
Result = Input Value × (Source Unit in Joules ÷ Target Unit in Joules)Every energy unit has a fixed conversion factor to joules (the SI base unit of energy). The converter first translates your input into joules, then converts from joules to the target unit.
Key Conversion Factors (to Joules)
Example: To convert 5 kWh (a typical Indian household's daily consumption for a small apartment) to kilocalories: 5 × 3,600,000 ÷ 4,186.8 = 4,299.23 kcal.
Assumptions: All conversion factors follow the thermochemical calorie definition (1 cal = 4.184 J) and the ISO 31 / NIST standard values. The BTU value used is the International Table BTU (1 BTU = 1,055.05585262 J).
Practical Examples
Monthly Electricity Bill in Mumbai
Input: 250 kWh (average 2BHK flat)
Result: 900,000,000 J (900 MJ)
Use Case: Understanding your monthly energy consumption in standard SI units for engineering comparisons or solar panel sizing.
Daily Calorie Intake to Kilojoules
Input: 2,000 kcal (recommended adult diet)
Result: 8,373.6 kJ
Use Case: Indian nutrition labels increasingly show kilojoule values alongside kcal. This helps you cross-verify packaged food labels.
AC Rating: BTU to Kilowatts
Input: 12,000 BTU (1-ton AC, common in India)
Result: 12,660,672 J (12.66 MJ), equivalent to 3.517 kWh of cooling per hour
Use Case: Comparing air conditioner specifications between Indian brands (often in tons) and international brands (in BTU or kW).
Industrial Natural Gas: Therms to MWh
Input: 500 therms (US gas utility bill)
Result: 14.65 MWh
Use Case: International businesses converting US natural gas billing units to metric electrical equivalents used in European or Indian energy audits.
What Is an Energy Converter?
An energy converter is a calculation tool that transforms a quantity of energy expressed in one unit into its equivalent in another unit. Energy is a fundamental physical quantity measured across many disciplines — physics, engineering, nutrition, electricity billing, and climate science — each of which historically adopted different measurement systems. This tool bridges those systems instantly.
This converter is designed for students studying thermodynamics or physics, engineers comparing fuel efficiencies, nutritionists cross-checking food labels between kcal and kJ, homeowners analyzing electricity bills, and professionals working across international measurement standards. It handles 15 units spanning SI (joule family), CGS (erg), Imperial (BTU, therm, foot-pound), electrical (watt-hour family), and atomic-scale (electronvolt) systems.
Use it when you need to compare energy quantities across different contexts — for example, understanding how many food calories your daily electricity consumption equals, or converting a gas furnace rating from BTU to kilowatts for an energy audit. The tool provides both a single target conversion and a complete multi-unit table showing all 15 equivalents at once.
Sources & Methodology
This converter uses conversion factors from the International System of Units (SI) as maintained by the Bureau International des Poids et Mesures (BIPM). The joule-to-calorie ratio follows the thermochemical definition (1 cal = 4.184 J). The BTU value uses the International Table definition (1 BTU = 1,055.05585262 J). The electronvolt value uses the 2019 SI redefinition exact value (1 eV = 1.602176634 × 10⁻¹⁹ J). All factors are constants — no approximations or rounding are applied before the final display formatting.
Important Considerations
While the mathematical conversion is exact, real-world energy comparisons involve context. Thermal energy (calories, BTU) and electrical energy (kWh) are physically interchangeable in theory, but conversion efficiency losses apply in practice. For instance, a 1 kWh electric heater delivers approximately 3,412 BTU of heat at near-100% efficiency, but a gas furnace rated at 3,412 BTU may only deliver 80–95% of that energy as usable heat. Keep efficiency factors in mind when using these conversions for equipment comparisons.
Frequently Asked Questions
Yes, this energy converter is 100% free to use with no hidden charges, no signup required, and no premium tier. You can perform unlimited conversions at any time.
Absolutely. All conversions are performed entirely in your browser using client-side JavaScript. No data is transmitted to any server, stored in cookies, or logged anywhere. Your input values never leave your device.
This converter uses internationally standardized conversion factors defined by the International System of Units (SI) and NIST. Results are accurate to at least 10 significant digits, matching the precision of IEEE 754 double-precision floating-point arithmetic used by modern browsers.
The converter supports 15 units: joule (J), kilojoule (kJ), megajoule (MJ), gigajoule (GJ), calorie (cal), kilocalorie (kcal), watt-hour (Wh), kilowatt-hour (kWh), megawatt-hour (MWh), British thermal unit (BTU), therm, foot-pound force (ft·lbf), electronvolt (eV), kilo-electronvolt (keV), and erg.
A calorie (cal) is the energy needed to raise 1 gram of water by 1°C. A kilocalorie (kcal) equals 1,000 calories and is the unit commonly labelled "Calories" on food packaging in India and worldwide. When a nutrition label says 200 Calories, it actually means 200 kcal.
Indian electricity bills measure consumption in kWh (units). One kWh equals 3,600,000 joules (3.6 MJ). Enter your kWh value, select kWh as the source unit, and choose joules as the target to get the exact conversion.
Yes. The converter handles values from extremely small (like electronvolts used in particle physics) to very large (like gigajoules or megawatt-hours used in power generation). Scientific notation is displayed automatically for results smaller than 0.001 or larger than 1 trillion.
A British Thermal Unit (BTU) is the energy required to raise one pound of water by one degree Fahrenheit. BTU is widely used in the United States for rating air conditioners, heaters, and furnaces. In India, AC capacity is often marketed in BTU alongside tonnage ratings.
Once the page is fully loaded, the converter works without an internet connection since all calculations run in your browser. However, you need an initial connection to load the page. You can save the page as an HTML file for true offline use.
Yes, the energy converter is fully responsive and optimized for smartphones, tablets, and desktops. All buttons and inputs meet minimum 44px touch targets for comfortable mobile use.