Energy Unit Converter (J, cal, kcal, kWh)

Converts energy into joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU and electronvolts. One calorie is 4.184 J, and the "calories" on food labels are really kilocalories.

Explanation

Enter an amount of energy and choose its unit, and every other unit follows. Kilocalories convert to joules exactly as easily as kilowatt-hours convert to kilocalories.

The definitions

1 cal = 4.184 J, the thermochemical calorie
1 kcal = 1000 cal = 4184 J
1 kWh = 3600000 J, a thousand watts for an hour
1 eV = 1.602176634 × 10⁻¹⁹ J, an exact value since the 2019 SI redefinition

Example

Convert one kilocalorie.

1\ \text{kcal} = 4184\ \text{J} = 1.1622\ \text{Wh}

Calories on food labels

The "200 calories" printed on a packet means 200 kcal, or 200,000 calories. In everyday speech, a "calorie" is almost always a kilocalorie.

A rice ball of about 180 kcal is 753 kJ — enough to run a 60 W bulb for three and a half hours. A daily intake of 2000 kcal is around 2.3 kWh, which as electricity would cost only a few tens of yen.

The scale of the electronvolt

The electronvolt belongs to atoms and particles: a single eV is just 1.6 × 10⁻¹⁹ J. It is worlds away from everyday energies, but it is exactly the right size down there — chemical bonds run to a few eV, and a photon of visible light carries two or three.