Type an amount of energy into any of the 11 units and all the others update together. Switch on scientific notation for tiny electron-volt or huge megajoule values, and see what the energy means in light bulbs, heaters and hot water.
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J
kJ
MJ
cal
kcal
Wh
kWh
BTU
thm
eV
ft·lbf
Common energy amounts (click to load)
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Energy conversion table
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How to use the Energy Converter
Type an energy value into any unit, for example 250 in Kilocalories or 3.5 in Kilowatt-hours.
Turn on scientific notation if you work with electron volts or very large amounts.
Read the headline for the usual pair (kcal ⇄ kJ, kWh ⇄ BTU) and the full grid below.
See the equivalents panel to picture the energy, or check the definitions used in the formula.
Download a table of any two units with your own start and step.
How energy conversion works
Every unit is defined as an exact number of joules (one joule is one newton of force over one meter, or one watt for one second). The converter computes result = value × J per source unit ÷ J per target unit. Example: 3.5 kWh × 3,600,000 = 12,600,000 J, and 12,600,000 J ÷ 1,055.06 = 11,942 BTU.
Power-based units come from energy = power × time: a watt-hour is 1 W for 3,600 s. That is why a 60 W bulb running for 10 hours uses 600 Wh, or 0.6 kWh, on your electricity bill.
Energy unit equivalents
Unit
Joules
Second view
Third view
1 kilocalorie (kcal, food Calorie)
4,184 J (exact)
1.16222 Wh
3.96567 BTU
1 calorie (cal)
4.184 J (exact)
0.00116222 Wh
0.00396567 BTU
1 watt-hour (Wh)
3,600 J (exact)
0.860421 kcal
3.41214 BTU
1 kilowatt-hour (kWh)
3.6 MJ (exact)
860.421 kcal
3,412.14 BTU
1 BTU (IT)
1,055.05585262 J
0.252164 kcal
0.293071 Wh
1 therm (US)
105.4804 MJ
29.3001 kWh
≈ 99,976 BTU (IT)
1 foot-pound (ft·lbf)
1.35582 J
0.000324048 kcal
0.00128507 BTU
1 electron volt (eV)
1.602176634 × 10⁻¹⁹ J (exact)
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Calorie and BTU variants
Calorie: this converter uses the thermochemical calorie (4.184 J), the basis of nutrition labels. The International Table calorie is 4.1868 J.
BTU: values use the International Table BTU (1,055.056 J). Older “59 °F” or “mean” BTUs differ by under 0.1%.
Therm: the US therm (105.4804 MJ) is used here; the EU therm is 105.506 MJ.
Power vs energy: kW and BTU/h are rates. Multiply by hours to get kWh or BTU before converting.
Frequently asked questions
How many joules are in a calorie?
One thermochemical calorie is exactly 4.184 J, so a food Calorie (1 kcal) is 4,184 J or 4.184 kJ. Some engineering tables use the International Table calorie of 4.1868 J, a 0.07% difference.
Is a food Calorie the same as a kilocalorie?
Yes. The Calorie on nutrition labels (capital C) is a kilocalorie: 1,000 small calories, or 4.184 kJ. Labels outside the US often list both kcal and kJ.
How many BTU are in a kilowatt-hour?
One kWh is about 3,412.14 BTU, because 1 kWh = 3,600,000 J and 1 BTU = 1,055.06 J. Heating and cooling equipment is often rated in BTU per hour.
What is a therm?
A US therm is 105,480,400 J, about 100,000 BTU or 29.3 kWh. US natural gas bills are often charged per therm.
How do I convert kWh to joules?
Multiply by 3,600,000. A kilowatt-hour is 1,000 watts for 3,600 seconds, so 2 kWh = 7.2 MJ.
What is an electron volt?
The energy an electron gains moving through one volt: exactly 1.602176634 × 10⁻¹⁹ J. It is used in atomic, particle and semiconductor physics.
Is a foot-pound of energy the same as a foot-pound of torque?
They share the same units (1 ft·lbf = 1.35582 J) but mean different things. Energy is force times distance moved; torque is force times lever arm. This converter treats ft·lbf as work or energy.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.