# Energy Converter > Convert between joules, calories, BTU, kilowatt-hours, and other energy units **Category:** Conversion **Keywords:** energy, joules, calories, BTU, kWh, watt-hours, conversion, converter **URL:** https://complete.tools/energy-converter ## How it calculates The energy converter uses the joule (J) as the base unit for all conversions, as it is the official SI unit of energy. Each conversion follows a two-step process: first, the input value is converted to joules using the specific conversion factor for that unit, then the joule value is converted to the target unit. The key conversion factors used are: • 1 calorie (cal) = 4.184 joules (thermochemical definition) • 1 kilocalorie (kcal) = 4,184 joules • 1 BTU = 1,055.06 joules (International Table BTU) • 1 kilowatt-hour (kWh) = 3,600,000 joules • 1 watt-hour (Wh) = 3,600 joules • 1 electronvolt (eV) = 1.602176634 × 10⁻¹⁹ joules • 1 foot-pound (ft-lb) = 1.3558179483314 joules The formula is: Result = Input × (From Unit Factor ÷ To Unit Factor). For example, converting 100 calories to kilojoules: 100 × (4.184 ÷ 1000) = 0.4184 kJ. These conversion factors are based on internationally accepted definitions from organizations like NIST and BIPM. ## Who should use this This energy converter serves a wide range of professionals and everyday users. Nutritionists and dietitians use it to convert between food calories (kilocalories) and joules when analyzing dietary requirements or comparing nutritional information from different countries. Engineers and HVAC technicians rely on BTU-to-joule conversions when designing heating and cooling systems or evaluating appliance efficiency. Electricians and energy auditors convert between kilowatt-hours and other units to calculate electricity costs and consumption patterns. Physics students and researchers work with electronvolts when studying atomic and particle physics, needing to convert to joules for energy calculations. Fitness enthusiasts and athletes convert calories to kilojoules when tracking exercise energy expenditure. Mechanical engineers use foot-pound conversions when calculating work done by machines or torque applications. Home energy managers convert between kWh and BTU to compare heating options or understand solar panel output. ## Worked examples Example 1: Converting food energy to joules. A nutrition label shows 250 kcal per serving. To convert to kilojoules: 250 kcal × 4.184 kJ/kcal = 1,046 kJ. This is useful when comparing food products labeled in different unit systems. Example 2: Calculating electricity costs. Your appliance uses 1,500 watts for 3 hours. Total energy: 1,500 W × 3 h = 4,500 Wh = 4.5 kWh. In joules: 4.5 × 3,600,000 = 16,200,000 J or 16.2 MJ. At $0.12 per kWh, the cost is $0.54. Example 3: HVAC calculation. A furnace produces 80,000 BTU/hour. Converting to kilowatts: 80,000 BTU × 1,055.06 J/BTU ÷ 3,600,000 J/kWh = 23.4 kW. This helps compare furnace output to electric heating alternatives. Example 4: Exercise energy. Running burns approximately 400 kcal in 30 minutes. Converting to joules: 400 × 4,184 = 1,673,600 J or 1.67 MJ. This equals about 0.46 kWh of energy expenditure. Example 5: Particle physics. An electron accelerated through 100 volts gains 100 eV of kinetic energy. In joules: 100 × 1.602 × 10⁻¹⁹ = 1.602 × 10⁻¹⁷ J. ## Limitations This converter has several important limitations to consider. First, it uses the thermochemical calorie (4.184 J) rather than other calorie definitions like the 15°C calorie or IT calorie, which differ slightly. For most practical purposes, this difference is negligible. Second, the electronvolt conversion involves extremely small numbers that may exceed display precision for very large input values. Third, the converter does not account for efficiency losses in real-world energy transformations, such as converting electrical energy to heat or mechanical work. Fourth, some units like BTU have multiple definitions (IT BTU, thermochemical BTU, mean BTU), and this tool uses the International Table definition. Fifth, the tool assumes ideal conversions and does not factor in real-world considerations like transmission losses or conversion efficiency. Finally, very large or very small numbers may display in scientific notation, which could be less intuitive for some users. ## FAQs **Q:** What is the difference between calories and kilocalories? **A:** The small calorie (cal) is used in chemistry and physics, while the kilocalorie (kcal) or food Calorie (with capital C) is used in nutrition. One kilocalorie equals 1,000 small calories. When a food label says "100 Calories," it means 100 kcal or 100,000 cal. **Q:** Why are there so many different energy units? **A:** Different fields developed their own convenient units before the SI system standardized on joules. BTU originated in heating industries, calories in chemistry, kilowatt-hours in electrical engineering, and electronvolts in particle physics. Each unit remains practical for its specific application. **Q:** How do I convert between electrical power and energy? **A:** Power (watts) measures energy flow rate, while energy (joules or watt-hours) measures total work. Multiply power by time to get energy: 100 watts × 2 hours = 200 watt-hours = 0.2 kWh = 720,000 joules. **Q:** What is a BTU used for in practice? **A:** BTU (British Thermal Unit) is commonly used in HVAC systems, water heater ratings, and natural gas billing. It represents the energy needed to raise one pound of water by one degree Fahrenheit. **Q:** Why is the joule the standard SI unit? **A:** The joule was chosen as the SI energy unit because it directly relates to mechanical work (1 J = 1 N·m) and electrical energy (1 J = 1 W·s), providing consistency across physics, engineering, and chemistry. **Q:** What are electronvolts used for? **A:** Electronvolts measure energy at the atomic and subatomic scale. One eV is the energy gained by an electron accelerated through a potential difference of one volt. Particle physicists use keV, MeV, and GeV for higher energies. --- *Generated from [complete.tools/energy-converter](https://complete.tools/energy-converter)*