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CalcChef

Energy Converter

Convert J, kJ, cal, kcal, Wh, kWh, MWh, BTU, therms, ft·lbf, erg and eV either way: 1 kWh = 3.6 MJ = 860.42 kcal = 3412.14 BTU = 0.0341 therm. How it works

Use the Energy Converter

Result
0.001 Kilojoules
Scientific 1e-3

1 Joule ≈ 0.001 Kilojoules

1 Joule in every energy unit
UnitValue
Kilojoules (kJ)0.001
Megajoules (MJ)0.000001
Calories (cal, thermochemical)0.2390057361
Kilocalories (kcal, food Calorie)0.0002390057361
Watt-hours (Wh)0.0002777777778
Kilowatt-hour (kWh)0.0000002777777778
Megawatt-hours (MWh)2.777777778e-10
Gigawatt-hours (GWh)2.777777778e-13
BTU (International Table)0.0009478171203
Electronvolt (eV)6241509074000000000
Megaelectronvolt (MeV)6241509074000
Ergs (erg)10000000
Therms (100,000 BTU)0.000000009478171203
Foot-pounds (ft-lbf)0.7375621493

About the Energy Converter

1 kWh = 3.6 MJ = 3,600,000 J = 860.4206501 kcal = 3412.141633 BTU. To turn kilocalories into kilojoules, multiply by 4.184, so a 2,000 Calorie day of food is 8368 kJ. This energy converter changes a value between joules, kilojoules, megajoules, calories, kilocalories, watt-hours, kilowatt-hours, megawatt-hours, gigawatt-hours, BTU, therms, foot-pounds, ergs, electronvolts and megaelectronvolts, in either direction.

One unit of energy in J, kJ, kcal, kWh and BTU

1 ofJkJkcalkWhBTU
1 J10.0010.00023900573610.00000027777777780.0009478171203
1 kJ100010.23900573610.00027777777780.9478171203
1 MJ10000001000239.00573610.2777777778947.8171203
1 cal4.1840.0041840.0010.0000011622222220.003965666831
1 kcal41844.18410.0011622222223.965666831
1 kWh36000003600860.420650113412.141633
1 BTU1055.0558531.0550558530.25216440070.00029307107021

Up to 10 significant digits, as the converter shows them. cal and kcal are the thermochemical calorie (4.184 J) and kilocalorie; BTU is the International Table BTU (1,055.05585262 J). 1 eV is 1.602176634e-19 J and 1 therm is 105505585.3 J.

How to use this tool

  1. Type the amount and choose its unit under From.
  2. Choose the unit you want under To. The swap button reverses the pair.
  3. Read the result. The line under it says what 1 of the From unit is in the To unit, and the copy menu gives the plain number, scientific notation or a sentence.

Frequently asked questions

How many joules are in a kWh?
3,600,000 J, or 3.6 MJ: one kilowatt is 1,000 joules every second, for 3,600 seconds. 10 kWh is 36 MJ.
Is a Calorie the same as a kilocalorie?
Yes. The Calorie with a capital C on a food label is the kilocalorie, 4,184 J or 4.184 kJ. The small calorie, cal in the unit list, is 1,000 times smaller at 4.184 J. 100 kcal is 418.4 kJ.
How do I convert kJ to kcal?
Divide by 4.184. A food label that says 500 kJ is 119.5028681 kcal, about 120 Calories.
How many kWh is a BTU, and a therm?
1 BTU is 0.0002930710702 kWh, so 1 kWh is 3412.141633 BTU. A therm is 100,000 BTU, which is 29.30710702 kWh, and Therms is in the unit list: 1.5 therms is 43.96066053 kWh. This is the therm US gas bills use. NIST SP 811 also lists a US therm built on the 59 °F BTU, about 0.02% smaller.
How many joules is a foot-pound?
1 ft·lbf is 1.355817948 J: one pound-force (4.4482216152605 N) acting through one foot (0.3048 m). Going the other way, 1 J is 0.7375621493 ft·lbf and 1 BTU is 778.1692623 ft·lbf.
Can I convert watt-hours, or kW to kWh?
Yes: Wh, MWh and GWh are in the list. A 50 Wh laptop battery is 0.05 kWh and 180 kJ, and 1 MWh is 1,000 kWh, or 3412141.633 BTU. Watts and kilowatts measure power, not energy, so they cannot be converted to kWh without a time: a 1 kW heater running for 1 hour uses 1 kWh.

Putting a gas bill and an electric bill on one scale

Gas is billed per therm and electricity per kWh. A therm is 100,000 BTU, which the converter gives as 29.30710702 kWh, so gas at $1.50 a therm is 1.50 ÷ 29.30710702 = $0.0512 per kWh of heat, before the furnace's own losses. Set that beside the price per kWh on an electric bill to compare a gas furnace with electric resistance heat.

The same idea works for food: the 2,000-calorie reference on US nutrition labels is 2.324444444 kWh, about what a 100 W bulb uses in a day. Watts, kilowatts and BTU per hour are power, not energy, and belong in the power converter.

Units and exact factors

Every conversion goes through joules: result = value × factor(from) ÷ factor(to).

  • kJ = 1,000 J and MJ = 1,000,000 J

  • cal (thermochemical) = 4.184 J and kcal = 4,184 J

  • Wh = 3,600 J and kWh = 3,600,000 J, so 1 kWh = 3.6 MJ = 860.4206501 kcal

  • MWh = 3.6 × 10⁹ J and GWh = 3.6 × 10¹² J, so 1 MWh = 1,000 kWh = 3412141.633 BTU

  • BTU (International Table) = 1,055.05585262 J, so 1 kWh = 3412.141633 BTU

  • eV = 1.602176634 × 10⁻¹⁹ J and MeV = 1.602176634 × 10⁻¹³ J

  • erg = 10⁻⁷ J (the CGS unit), so 1 J = 10000000 erg

  • ft·lbf = 0.3048 m × 4.4482216152605 N = 1.3558179483314004 J, so 1 BTU = 778.1692623 ft·lbf

  • therm = 100,000 BTU = 105,505,585.262 J, so 1 therm = 29.30710702 kWh

Results keep up to 10 significant digits with trailing zeros removed, and values below a billionth switch to exponent form. Older tables sometimes use the thermochemical BTU (about 1,054.35 J), roughly 0.07% smaller than the one here. The therm here is the 100,000 BTU therm on gas bills, which NIST SP 811 lists as the EC therm; its US therm, built on the 59 °F BTU, is 1.054804 × 10⁸ J, about 0.02% smaller. MJ per kilogram and tonnes of oil equivalent are not in the list.

Fun Fact: Since the 2019 redefinition of the SI fixed the charge of the electron, the electronvolt is exactly 1.602176634 × 10⁻¹⁹ joules, with no measurement uncertainty.

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