Instantly convert between joules, kilojoules, calories, kWh, eV, BTU, and ft·lb
Energy is the capacity to do work or produce heat. Our converter handles all major energy units used in science, engineering, nutrition, and everyday life. From the SI standard joule to food calories and electricity billing units, you can convert between any of these quickly and accurately.
| Unit | Equivalent in Joules |
|---|---|
| J (Joule) | 1 J |
| kJ (Kilojoule) | 1,000 J |
| cal (Calorie) | 4.184 J |
| kcal (Kilocalorie) | 4,184 J |
| Wh (Watt-hour) | 3,600 J |
| kWh (Kilowatt-hour) | 3,600,000 J |
| eV (Electronvolt) | 1.602 × 10⁻¹⁹ J |
| BTU | 1,055.06 J |
| ft·lb (Foot-pound) | 1.355818 J |
A joule (J) is the SI unit of energy, representing the energy transferred when a force of one newton acts over one meter. It is equivalent to the energy needed to lift a small apple one meter against Earth's gravity.
One kilocalorie (kcal) equals 1,000 calories (cal). In nutrition, a 'Calorie' with capital C actually refers to a kilocalorie. 1 kcal ≈ 4.184 kilojoules.
A watt-hour (Wh) is the energy produced by one watt of power for one hour. A kilowatt-hour (kWh) equals 1,000 watt-hours and is the standard unit used on electricity bills. 1 kWh = 3.6 megajoules.
One BTU (British Thermal Unit) equals approximately 1,055 joules. BTU is commonly used in HVAC systems and to describe heating values of fuels. 1 BTU ≈ 252 cal.
An electronvolt (eV) is the energy gained by an electron when accelerated through one volt. It is commonly used in atomic and particle physics. 1 eV ≈ 1.602 × 10⁻¹⁹ joules.