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Energy converter

Joules, kilojoules, calories and kilocalories, watt-hours and kWh, BTU, foot-pounds and electronvolts.

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Fromkilocalorie (food Calorie) (kcal)
1
Tokilojoule (kJ)
4.184
DecimalsAuto (up to 10 significant digits)

Formula: kJ = kcal × 4.184

1 kcal = 4.184 kJ

Common values: kilocalorie (food Calorie) to kilojoule

kcalkJ
1 kcal4.184 kJ
10 kcal41.84 kJ
50 kcal209.2 kJ
100 kcal418.4 kJ
200 kcal836.8 kJ
250 kcal1,046 kJ
500 kcal2,092 kJ
1,000 kcal4,184 kJ
2,000 kcal8,368 kJ
2,500 kcal10,460 kJ

How it works

Energy appears on food labels (kcal and kJ), electricity bills (kWh), gas and air-conditioning specs (BTU), physics homework (joules, electronvolts) and engineering (foot-pounds). This converter takes any of them.

The food "Calorie" is a kilocalorie. This converter uses the thermochemical calorie, exactly 4.184 J, so 1 kcal = 4.184 kJ; the International Table calorie (4.1868 J) differs by 0.07%. A watt-hour is 3600 J, so 1 kWh = 3.6 MJ. The International Table BTU is 1055.05585262 J, which makes 1 kWh ≈ 3412.14 BTU. The electronvolt is exactly 1.602176634 × 10⁻¹⁹ J since the 2019 SI redefinition.

Energy is not power: kWh measures an amount of energy, kW measures the rate. Use the power converter for kW, hp or BTU per hour.

Common energy conversions

Food energy is labelled in kilocalories (the "Calorie" on US labels) and kilojoules; electricity is billed in kilowatt-hours; heating and air conditioning often use BTU.

  • 1 kcal = 4.184 kJ (kJ = kcal × 4.184)
  • 1 kJ = 0.2390057361 kcal (kcal = kJ × 0.239005736138)
  • 1 kWh = 3.6 MJ (MJ = kWh × 3.6)
  • 1 BTU = 1.055055853 kJ (kJ = BTU × 1.05505585262)
  • 1 kWh = 3,412.141633 BTU (BTU = kWh × 3,412.14163313)
  • 1 Wh = 3,600 J (J = Wh × 3,600)

Every energy unit in this converter

The size of each unit in joules (J), the base unit the converter uses internally. Values are exact where the unit has an exact definition.

UnitIn J
joule (J)1 J
kilojoule (kJ)1,000 J
megajoule (MJ)1,000,000 J
calorie (thermochemical) (cal)4.184 J
kilocalorie (food Calorie) (kcal)4,184 J
watt-hour (Wh)3,600 J
kilowatt-hour (kWh)3,600,000 J
British thermal unit (IT) (BTU)1,055.055853 J
foot-pound force (ft·lbf)1.355817948 J
electronvolt (eV)1.602176634e-19 J

How to use it

  1. Choose the energy unit you have and the one you want.
  2. Type the value in either box.
  3. Read the formula, or use the table for common amounts.

Frequently asked questions

How many kJ are in a kcal?

Exactly 4.184 kJ per kcal (thermochemical). A 2000 kcal daily intake is 8368 kJ.

Is a food Calorie the same as a calorie?

No. A food Calorie (capital C) is a kilocalorie, 1000 small calories. Nutrition labels that say "Calories" or "kcal" mean the same thing.

How many BTU are in a kWh?

About 3412.14 BTU (IT). Heating and cooling equipment is often rated in BTU per hour; use the power converter for that.

How many kWh does a 2 kW heater use in 3 hours?

Energy = power × time = 2 kW × 3 h = 6 kWh. Multiply by your tariff per kWh to estimate the cost.

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