Common Energy Units
This converter supports commonly used units including:
- Joules (J)
- Kilojoules (kJ)
- Calories (cal)
- Kilocalories (kcal)
- Watt-hours (Wh)
- Kilowatt-hours (kWh)
- British thermal units (BTU)
When to Convert Energy Units
Energy conversion is useful for electricity, heating, nutrition, physics, engineering, appliances, fuel use, and scientific calculations. An online converter helps reduce manual calculation errors and makes it easier to compare values expressed in different units.
Energy Conversion FAQ
What is energy?
Energy is the capacity to perform work or cause change. It can appear as mechanical, electrical, thermal, chemical, nuclear, or radiant energy, and it can be expressed using units such as joules, watt-hours, calories, and British thermal units.
What is the SI unit of energy?
The joule, with the symbol J, is the SI-derived unit of energy. One joule equals the work performed when a force of one newton moves an object through one meter.
How do I convert between energy units?
Multiply the original value by its joule conversion factor and then divide by the joule factor of the target unit. Using joules as the common reference works for mechanical, electrical, thermal, and other energy units.
What is the general energy conversion formula?
Use target value = original value × source-unit factor ÷ target-unit factor, where both factors express the units in joules.
What is the difference between a watt and a watt-hour?
A watt measures power, which is the rate at which energy is transferred or used. A watt-hour measures energy. Watts cannot be converted directly to watt-hours without knowing the operating time.
How do I calculate energy from power and time?
Multiply power by time using compatible units: Energy = Power × Time. For example, a 100 W device operating for 5 hours uses 500 Wh, or 0.5 kWh.
Can kilowatts be converted directly to kilowatt-hours?
No. Kilowatts measure power and kilowatt-hours measure energy. The operating time is required. A 2 kW appliance operating for 3 hours uses 6 kWh.
What is the difference between a calorie and a food Calorie?
A lowercase calorie, written cal, is a small energy unit. A food Calorie, often written with an uppercase C, normally means one kilocalorie: 1 Calorie = 1 kcal = 1,000 cal.
Is a foot-pound of energy the same as a pound-foot of torque?
No. They may have the same dimensional components, but energy and torque represent different physical quantities. A converter should not treat torque values as energy values without considering the physical context.
What is an electronvolt?
An electronvolt, written eV, is a small energy unit commonly used in atomic, particle, and semiconductor physics. One electronvolt equals exactly 1.602176634 × 10−19 joules.
Why are there different units for the same amount of energy?
Different industries developed units suited to their work. Joules are standard in science, kilowatt-hours are common for electricity, calories and kilojoules are used for food energy, BTUs are used for heating and cooling, and electronvolts are used in atomic physics.
Why might two energy converters show slightly different results?
Differences can result from rounding or from using different definitions of units such as the calorie or BTU. Check the exact unit variant and conversion factor when precision is important.
Are energy conversion factors always exact?
Some factors are defined exactly, including 1 Wh = 3,600 J and 1 thermochemical calorie = 4.184 J. Other displayed factors may be approximate or depend on the specific historical unit definition.