Energy Converter

Convert between joules, calories, kilowatt-hours, BTU, and other energy units. Ideal for physics, engineering, nutrition, and electricity calculations.

How to Use

  1. Enter the energy value

    Type the energy value you want to convert.

  2. Select the units

    Choose the source unit (e.g., kWh) and the target unit (e.g., joules).

  3. View the result

    Click Convert to see the converted energy value.

What are energy units?

Energy is the capacity to do work or produce heat. Because different fields have historically measured it with different units, conversion is often necessary. The base unit of energy in the International System (SI) is the joule (J), where 1 J equals the work done when a force of 1 N moves an object 1 m.

This converter processes every unit by first expressing it in joules (J), and it supports the following units.

  • cal / kcal — heat and nutrition. Food 'Calories' are actually kcal.
  • Wh / kWh — electrical energy and electricity billing
  • BTU — heating, cooling, and HVAC equipment ratings
  • eV — tiny energies at the atomic and subatomic scale
  • ft·lbf — the unit of work in imperial mechanical engineering

Conversion Formula

Every conversion works by expressing the input unit in the base unit (joules) and then dividing by the target unit's factor.

result = value × (joule factor of the source unit) ÷ (joule factor of the target unit)

For example, to convert 2 kWh to kcal, the kWh factor is 3,600,000 and the kcal factor is 4,184, so:

2 × 3,600,000 ÷ 4,184 = 1,720.84 kcal

Here, a conversion factor means how many joules (J) one unit corresponds to (for example, 1 cal = 4.184 J, 1 BTU = 1,055.06 J).

Frequently Asked Questions

What is the relationship between joules and calories?
One calorie (cal) is exactly 4.184 joules (J). This value is based on the thermochemical calorie, defined as the heat needed to raise the temperature of 1 g of water by 1°C.
What is the difference between a calorie and a kilocalorie?
One kilocalorie (kcal) equals 1,000 calories (cal). The 'Calorie' used in everyday food labeling actually means kcal, and 1 kcal = 4,184 J.
How do I convert kWh to joules?
1 kWh = 3,600,000 J (3.6 MJ). Using 1 watt of power for 1 hour is 3,600 J, and a kilowatt-hour is 1,000 times that. kWh is mainly used for electricity billing.
How many calories (kcal) are in 1 kWh?
One kilowatt-hour (kWh) is about 860,421 calories (cal), or roughly 860.42 kilocalories (kcal). It is calculated by dividing 3,600,000 J by 4,184 J (1 kcal).
What is a BTU?
A BTU (British Thermal Unit) is the energy needed to raise the temperature of one pound of water by 1°F. One BTU is approximately 1,055.06 J, and it is mainly used to rate the capacity of heating and cooling equipment such as air conditioners and boilers.
What is the electronvolt (eV)?
The electronvolt (eV) is the energy gained by a single electron moving through a potential difference of 1 volt, where 1 eV ≈ 1.602×10⁻¹⁹ J. It is used in physics and chemistry to handle the very small energies of atoms, molecules, and subatomic particles.
What is a foot-pound force (ft·lbf)?
One foot-pound force (ft·lbf) is the work done when a force of one pound-force moves an object one foot, equal to about 1.35582 J. It is used in imperial mechanical engineering to express torque and work.
How are energy and power different?
Power (W) is energy per unit of time and shows 'how fast' work is done, while energy (J, kWh) represents the 'total amount'. Since energy = power × time, running a 1 kW appliance for 1 hour consumes 1 kWh.
2026 international standards

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