SI unit for energy
Big energies
Ton of TNT
tons of TNT
Microscopic world
Reciprocal length

With our energy conversion calculator, you can convert energy between a wide range of various units. The magnitude of energy differs significantly in various aspects of life: from the low energies at the microscopic level of atoms to the enormous energies of nuclear bombs. That's why people have introduced many alternative units of energy. You might use our energy conversion calculator in different ways, depending on your needs. In the text below, you will find an explanation of how you can convert between some basic energy units, such as:

  • joules to kcal,
  • joules to kWh,
  • joules to eV.

We have also provided a possibility to compute less frequently used units, like tons of TNT to joules or therms to joules. Did you know that energy can be expressed in units of weight, temperature, or length? Read on if you want to know how our energy converter:

  • converts mass to energy,
  • converts temperature to energy,
  • converts length to energy.

Joules to kcal and kcal to joules conversion

Kilocalories (kcal) usually measure food energy. One calorie is the amount of thermal energy which is necessary to raise the temperature of water by one degree (in the temperature of 14.5 degrees Celsius). Knowing this, you can compute what is the equivalent value of kilocalorie expressed in joules, for example with our specific heat calculator. The result is:

1 kcal = 4184 J

and conversely

1 J ≈ 0.000239 kcal

Joules to kWh and kWh to joules conversion

Kilowatt-hours (kWh) are used in everyday electricity. It corresponds to the amount of energy consumed by a device within 1 hour with the power of 1000 watts (one kilowatt). Therefore, we can write:

1 kWh = 1 kW * 1 h = 1000 W * 3600 s = 3 600 000 J = 3.6 MJ and conversely 1 MJ ≈ 0.278 kWh

Do you know how much your electric energy costs? Check our electricity cost calculator to find out the annual electricity cost in a straightforward way.

Joules to eV and eV to joules conversion

In physics and chemistry, we often need to use very small energies to describe phenomena on the atomic scale. For that purpose, we can use a convenient unit called electronvolt (eV). One electronvolt is the energy obtained (or lost) by an electron that has traveled in an electric field with a potential difference of 1 volt. This energy equals:

1 eV = 1e * 1V ≈ 1.60217 * 10^(-19) C * V = 1.60217 * 10^(-19) J and conversely 1 J ≈ 6.2415 * 10^18 eV

In the above equation, e ≈ 1.60217 * 10^(-19) C is the elementary charge of an electron. Make sure to check our acceleration in the electric field calculator too, where you can estimate the acceleration of any charged particle in the electric field.

Tons of TNT and therms to joules

A ton of TNT is the energy unit which is the basic parameter of nuclear weapons, but it is also used to determine the strength of other events, such as meteorite impacts. One gram of TNT releases from 4100 to 4600 joules of energy from the explosion; it is conventionally assumed that it is exactly 4184 J. Therefore:

1 ton of TNT = 1 t * 4184 J/g = 1 000 000 g * 4184 J/g = 4.184 GJ = 1 Gcal

A therm is a unit of heat energy which is equivalent to burning 100 cubic feet (or 2.83 cubic meters) of natural gas. Therm is usually used by natural gas companies to calculate the actual energy use. This energy unit is useful for them because it depends only on the composition of the gas (and not on pressure or temperature). The conversion to joules is shown below:

1 therm ≈ 105.5 MJ

Mass to energy conversion

Sadly we're not gonna talk about how burn calories to lose weight, but rather about the equivalence between mass and energy in physics. You probably heard about the famous E = mc2 equation. Albert Einstein has proposed that every mass in the world is just energy waiting to be set free. Although it is not achievable yet, we can use this formula to express the energy in the units of weight. The 1 J of energy "weights":

m = E/c² ≈ (1 J)/(2.998 * 10^8 m/s)² ≈ 1.113 * 10^(-17) kg

where c ≈ 2.998 * 10^8 m/s is the light speed. This unit of energy is, for example, used to describe the annihilation process where an electron (with the mass me = 9.109 * 10^(-31) kg) collides with a positron (particle with the same mass but opposite charge) and creates two photons with the energy 1.022 MeV in total. You can check it with our energy conversion calculator! Just remember that electron and positron will have the mass of 2 me in total.

Temperature to energy conversion

In the classical kinetic theory of gases, the average kinetic energy per one particle is proportional to the product kB * T, where T is the temperature and kB ≈ 1.3806 * 10^(-23) J/K is the Boltzmann constant. Therefore, we can say that 1 J of energy has the temperature of:

T = E/kB = (1 J)/(1.3806 * 10^(-23) J/K) = 7.2432 * 10^22 K

We sometimes use this unit of energy in physics or chemistry. For example, when we want to describe the magnitude of thermal vibrations in the crystal lattice of the material. If we say that the energy of vibrating atoms is 200 K, it means that their vibrational energy is 17.235 meV(check it with our energy converter). We also encourage you to see our ideal gas law calculator!

Length to energy conversion

One of the central parts of the theory of quantum mechanics are matter waves. Every moving particle with specific kinetic energy behaves like a wave and can be described as having a certain wavelength. Check our De Broglie wavelength calculator to learn more about it. In spectroscopy (the study of the interaction between matter and waves) it is common to measure the energy of particle or light in units of reciprocal centimeters (cm⁻¹). The formula for appropriate conversion is provided by the Planck's equation:

E = h * c / λ

where h = 6.6261 * 10^(-34) m² kg /s is the Planck constant, c ≈ 2.998 * 10^8 m/s is the light speed and λ is the wavelength. If we write down above equation in different form, we can say that 1 J of energy will have:

1/λ = E / h * c = (1 J)/(6.6261 * 10^(-34) m² kg /s * 2.998 * 10^8 m/s) = 5.034 * 10^(24) m⁻¹ = 5.034 * 10^(22) cm⁻¹

You can check with our energy conversion calculator that a reciprocal centimeter describes rather low energies. For example, 50 meV = 403.28 cm⁻¹.

Dominik Czernia, PhD candidate