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Energy Converter

Popular Energy unit conversions

Energy Converter — Convert Joules, kWh, Calories, BTU & More

Our free online Energy Converter lets you instantly convert between 50+ units of energy — from everyday units like kilowatt-hours and calories to scientific units like electron-volts and ergs. Whether you need to convert joules to calories, kWh to joules, BTU to kilojoules, or kilocalories to megajoules, this tool delivers fast and highly accurate results.

Energy is the capacity to do work or produce heat. It appears in many forms — electrical, thermal, mechanical, chemical, nuclear — and is measured in different units depending on the field:

  • SI metric: joule (J), kilojoule (kJ), megajoule (MJ), gigajoule (GJ)
  • Electrical: kilowatt-hour (kWh), watt-hour (Wh), megawatt-hour (MWh)
  • Thermal: calorie (cal), kilocalorie (kcal), BTU (British Thermal Unit), therm
  • Mechanical: foot-pound, newton-meter, erg
  • Atomic: electron-volt (eV), kiloelectron-volt (keV), megaelectron-volt (MeV)
  • Explosive: ton of TNT, kiloton, megaton, gigaton

All conversions use internationally standardized SI factors and high-precision arithmetic, reliable for physics, electrical engineering, nutrition, chemistry, and everyday energy calculations.

Common Energy Conversion Reference

Here are the most frequently used energy conversions for quick reference:

  • 1 kilowatt-hour (kWh) = 3,600,000 joules = 3,600 kJ = 860.421 kcal = 3,412.14 BTU
  • 1 calorie (nutritional / food Cal) = 4,186.8 joules = 4.1868 kJ
  • 1 BTU (IT) = 1,055.06 joules = 1.05506 kJ = 0.000293 kWh
  • 1 joule = 0.239006 calories (thermochemical) = 0.000948 BTU
  • 1 kilojoule = 1,000 joules = 0.239006 kcal = 0.948 BTU
  • 1 electron-volt (eV) = 1.60218 × 10⁻¹⁹ joules
  • 1 ton of TNT = 4.184 × 10⁹ joules = 4.184 GJ
  • 1 therm = 105,505,600 joules = 29.3 kWh = 100,000 BTU

Frequently Asked Questions — Energy Converter

Question: How do I use the Energy Converter?

Answer: Select the unit you are converting from in the left list and the unit to convert to in the right list, then type your value. The result appears instantly across all listed units.

Question: What is a joule?

Answer: The joule (J) is the SI unit of energy, defined as the energy transferred when a force of one newton acts over a distance of one meter (J = N·m). It is the base unit for all energy measurements in the metric system.

Question: How many joules are in a kilowatt-hour?

Answer: One kilowatt-hour (kWh) equals exactly 3,600,000 joules (3.6 megajoules). A kWh is the unit used on electricity bills — it represents using 1,000 watts for one hour.

Question: What is the difference between a calorie and a kilocalorie?

Answer: A small calorie (cal) is the energy needed to raise 1 gram of water by 1°C ≈ 4.184 joules. A kilocalorie (kcal) equals 1,000 calories ≈ 4,184 joules. Food energy is measured in kilocalories (kcal), often labeled "Calories" (capital C) on nutrition labels.

Question: How do I convert BTU to kilowatt-hours?

Answer: Divide the BTU value by 3,412.14 to get kilowatt-hours. For example, 10,000 BTU ÷ 3,412.14 = 2.93 kWh. One BTU equals 1,055.06 joules or 0.000293 kWh.

Question: What is an electron-volt (eV)?

Answer: An electron-volt is the energy gained by an electron moving through an electric potential difference of one volt. It equals approximately 1.60218 × 10⁻¹⁹ joules. It is the standard unit of energy in atomic and particle physics.

Question: How many calories are in a kilowatt-hour?

Answer: One kilowatt-hour equals approximately 860,421 calories (thermochemical) or 859,845 kilocalories. Put another way, one kWh can raise the temperature of about 860 liters of water by 1°C.

Question: What is a BTU (British Thermal Unit)?

Answer: One BTU is the energy required to raise the temperature of one pound of water by 1°F. 1 BTU (IT) = 1,055.06 joules = 0.293 watt-hours. BTUs are used in the US for heating, cooling, and air conditioning system ratings.

Question: How accurate are the energy conversions in this tool?

Answer: All conversions use internationally standardized conversion factors with up to 12 significant digits of precision, suitable for electrical engineering, physics, chemistry, nutrition, and industrial applications.