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Convert between joules, calories, kWh, BTU, megajoules, and watt-hours instantly. Enter a value and see all conversions in real-time.
1 J = 0.239006 cal
1 cal = 4.184 J
1 J = 0.00000027778 kWh
1 kWh = 3,600,000 J
1 J = 0.000947817 BTU
1 BTU = 1055.06 J
1 J = 0.000277778 Wh
1 Wh = 3600 J
1 J = 0.000001 MJ
1 MJ = 1,000,000 J
1 kcal = 1000 cal
1 cal = 0.001 kcal
The joule (J) is the International System of Units (SI) base unit of energy. Named after physicist James Prescott Joule, it's defined as the energy transferred when one newton of force moves an object one meter. Joules are fundamental in physics and provide a common reference for all energy measurements.
Small calories (cal) measure heat energy in chemistry and physics, while food "Calories" (capital C) are actually kilocalories (kcal), equal to 1000 small calories. When a food label says 200 Calories, it means 200 kcal or 836,800 joules. This distinction is crucial when converting between nutritional and scientific energy measurements.
Kilowatt-hours (kWh) are the standard unit for electricity billing. One kWh equals 3.6 million joules and represents the energy consumed by a 1000-watt appliance running for one hour. Watt-hours (Wh) are commonly used for battery capacity in electronics and electric vehicles. Understanding these units helps you analyze energy costs and battery performance.
British Thermal Units (BTU) are traditional units still widely used in the United States for rating HVAC systems, furnaces, and air conditioners. One BTU is the energy needed to heat one pound of water by one degree Fahrenheit. While not an SI unit, BTU remains important for understanding heating and cooling capacity in residential and commercial applications.
Different fields prefer different energy units: physics uses joules, nutrition uses kilocalories, electrical engineering uses kWh and Wh, HVAC uses BTU, and large-scale energy systems use megajoules (MJ). This multi-unit converter allows you to bridge these domains and understand energy in any context, whether you're calculating food energy, electricity bills, or thermodynamic processes.
Choose based on your context: joules for physics, calories for chemistry, kilocalories for nutrition, kWh for electricity bills, Wh for batteries, BTU for HVAC systems, and megajoules for large-scale energy analysis. This converter lets you work in any unit and see equivalent values in all others.
These conversions use internationally recognized standard values: 1 cal = 4.184 J (thermochemical calorie), 1 BTU = 1055.06 J (ISO standard), and 1 kWh = 3,600,000 J (exact definition). Results are displayed with appropriate precision for practical use.
It depends on the field. Scientific work primarily uses joules. Nutrition uses kilocalories. Electricity providers use kWh. HVAC professionals use BTU. Each industry has adopted the most practical unit for its typical energy scales. The joule, being the SI unit, provides the universal standard.
Convert food Calories (kcal) to kWh by dividing by 860. For example, 2000 Calories = 2000 kcal ≈ 2.33 kWh. At $0.12 per kWh, that's about $0.28 of electricity. This shows food energy is quite cheap compared to most electricity rates, though the human body is not 100% efficient at converting food to work.