Energy Converter
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By Dr. Sarah ChenReviewed by Prof. David Okafor, PhD (Physics)Published: Updated:
References
- [1]National Institute of Standards and Technology (NIST), Guide for the Use of the International System of Units (SI), 2008. https://physics.nist.gov/cuu/pdf/sp811.pdf
- [2]International Organization for Standardization, ISO 80000-5: Quantities and Units – Part 5: Thermodynamics, 2019.
- [3]International Association for the Properties of Water and Steam (IAPWS), International Steam Table Properties of Water and Steam, 2018.
How to Use?
- 1
Enter the energy value
Type the numeric energy amount into the Energy Value field.
- 2
Select the source unit
Choose the unit of your input value from the unit dropdown: J, kJ, MJ, cal, kcal, kWh, BTU, eV, keV, or MeV.
- 3
Choose the display unit
Use the Display Result In dropdown to select which unit appears highlighted as the primary result.
- 4
Review all equivalent values
The result panel shows your value in the chosen display unit, with all other supported units listed as alternatives below.
- 5
Check for calorie vs Calorie ambiguity
Remember that food "calories" are actually kilocalories (kcal). 1 food Cal = 1 kcal = 4,184 J. This converter uses the small calorie (cal) for scientific accuracy.
- 6
Use related converters
For area or length unit conversions, use the Area Converter and Length Converter linked on this page.
Worked Examples
1Convert 1 kWh to joules
Given Values
energyValue:1
energyValue_unit:kWh
Results
J:3600000
2Convert 500 calories to kilojoules
Given Values
energyValue:500
energyValue_unit:cal
Results
J:2092
3Convert 100,000 BTU to kWh
Given Values
energyValue:100000
energyValue_unit:BTU
Results
J:105506000
4Convert 1,000 J to kilocalories
Given Values
energyValue:1000
energyValue_unit:J
Results
J:1000
5Convert 2,000 kcal to megajoules
Given Values
energyValue:2000
energyValue_unit:kcal
Results
J:8368000
6Convert 1 MeV to joules
Given Values
energyValue:1
energyValue_unit:MeV
Results
J:1.602176634e-13
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Frequently Asked Questions
In nutrition, 1 Calorie (kcal, capital C) = 1,000 small calories (cal). This converter uses the small calorie (cal = 4.184 J) for scientific consistency. A food label saying 200 Calories contains 200,000 small calories or 836,800 J.
British Thermal Unit (BTU) is the energy needed to raise one pound of water by one degree Fahrenheit. One BTU equals approximately 1,055.06 J. BTUs are used primarily in heating, ventilation, and air conditioning (HVAC) to rate equipment capacity. A typical residential furnace is rated at 60,000 to 100,000 BTU per hour.
One small calorie (cal) = 4.184 J exactly (thermochemical calorie). One food Calorie (kcal) = 4,184 J. The thermochemical calorie is the standard used by this converter and recommended by IUPAC for scientific work.
Energy (kWh) = Power (kW) × Time (h). A 100 W (0.1 kW) bulb on for 10 hours uses 1 kWh of energy. Watts are a unit of power, while watt-hours are a unit of energy. The energy converter handles both watt-hour and joule-based conversions.
BTU (British Thermal Unit) is the standard unit for heating and cooling capacity in the United States and United Kingdom. Furnaces, boilers, water heaters, and air conditioners are rated in BTU per hour. One BTU approximately equals the heat released by burning a single wooden match. Room air conditioners typically range from 5,000 to 15,000 BTU/h.
An average adult consumes about 8,700 kJ (2,080 kcal) per day, which equals approximately 8,700,000 J. This energy is used for metabolism, physical activity, and basic bodily functions. Athletes and physically active individuals may require 10,500 to 12,500 kJ or more daily.
A kilowatt (kW) is a unit of power – the rate of energy use. A kilowatt-hour (kWh) is a unit of energy – the amount of energy used over time. If a 2 kW appliance runs for 3 hours, it consumes 6 kWh of energy. Electricity bills charge you for energy (kWh), not power (kW). The distinction is critical for understanding both billing and equipment specifications.
1 watt = 3.412 BTU/hour. To convert watts to BTU/h, multiply by 3.412. To convert BTU/h to watts, divide by 3.412. This is useful for comparing the power ratings of appliances and HVAC equipment across different measurement systems. For example, a 10,000 BTU/h air conditioner draws approximately 2,930 W of power.
1 kWh = 3,600,000 J exactly. This is the standard conversion used by electric utilities worldwide. The calculation is 1,000 W × 3,600 s = 3,600,000 J. To convert kWh to megajoules (MJ), multiply by 3.6. A typical US household consuming 900 kWh per month uses 3,240 MJ of electrical energy.
1 therm = 100,000 BTU. Therms are used for natural gas billing in the United States. One therm of natural gas contains approximately 105.5 MJ of energy. The average US home uses about 50 to 150 therms per month for heating, water heating, and cooking, depending on climate and appliance efficiency.
Food energy is measured using bomb calorimetry, which burns the food sample in an oxygen-rich chamber and measures the heat released. The Atwater system then adjusts the gross energy to account for digestibility: protein and carbohydrate contribute 4 kcal/g, fat contributes 9 kcal/g, and alcohol contributes 7 kcal/g. These standard factors are used worldwide for nutrition labelling. 1 food Calorie = 1 kcal = 4,184 J.
One joule is a small amount of energy by human standards. Lifting a small apple (100 g) one metre against gravity requires about 1 J. A heartbeat consumes roughly 0.5 J. A 60 W light bulb consumes 60 J per second. One food Calorie (kcal) equals 4,184 J, which is why food energy is measured in Calories – the same energy in joules would require large, impractical numbers.
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