How many joules are in a calorie?

One small calorie equals 4.184 joules. One food calorie (kilocalorie or kcal) equals 4,184 joules. When food labels say '100 Calories,' they mean 100 kcal or 418,400 joules.

How do I convert kWh to joules?

To convert kilowatt-hours to joules, multiply by 3,600,000 (3.6 million). For example, 1 kWh = 3,600,000 J = 3.6 MJ. This is because 1 kW = 1,000 J/s and 1 hour = 3,600 seconds.

What is the difference between a calorie and a kilocalorie?

A kilocalorie (kcal) equals 1,000 small calories. In nutrition, 'Calorie' (capital C) typically means kilocalorie. So a food with '100 Calories' contains 100 kcal or 100,000 small calories.

How many BTU are in a kWh?

One kilowatt-hour equals approximately 3,412 BTU. This conversion is important for comparing electrical and heating energy costs.

What is an electronvolt?

An electronvolt (eV) is the energy gained by an electron moving through a potential difference of 1 volt. It equals 1.602×10⁻¹⁹ joules. It's used in atomic, nuclear, and particle physics.

Énergie Converter

About Energy Conversion

Energy is the capacity to do work, one of the most fundamental concepts in physics and essential to understanding everything from nutrition to nuclear power. It appears in many forms—kinetic, potential, thermal, electrical, chemical, and nuclear—and can be converted from one form to another but never created or destroyed (conservation of energy).

Different fields use different energy units based on historical development and practical convenience: joules (J) in physics and engineering, calories in nutrition and chemistry, kilowatt-hours (kWh) for electricity billing, BTU (British Thermal Units) for heating and cooling in the US, and electronvolts (eV) in atomic and particle physics.

Our energy converter handles all common units across scientific, nutritional, and practical applications, making it easy to compare energy costs, understand food labels, or work through physics problems.

Common Energy Conversions

From	To	Multiply By
Joules	Calories (small)	0.2390
Calories (small)	Joules	4.184
kWh	Joules	3,600,000
Joules	kWh	2.778×10⁻⁷
BTU	Joules	1,055
kWh	BTU	3,412
kcal (food cal)	kJ	4.184
Watt-hours	Joules	3,600
eV	Joules	1.602×10⁻¹⁹
Therms	BTU	100,000

Energy Unit Reference

Joule (J) – The SI unit of energy, defined as 1 newton-meter or 1 watt-second. Named after James Prescott Joule. Used universally in physics and engineering for all energy calculations.

Kilojoule (kJ) – 1,000 joules. Common in nutrition labels outside the US (food energy is often shown in both kJ and kcal). 1 kcal = 4.184 kJ.

Calorie (cal) – Small calorie: the energy needed to heat 1 gram of water by 1°C. 1 cal = 4.184 J exactly (thermochemical calorie). Used in chemistry and physics.

Kilocalorie (kcal) – Food calorie: the energy to heat 1 kilogram of water by 1°C. 1 kcal = 4,184 J = 4.184 kJ. This is what nutrition labels call a "Calorie" (with capital C).

Kilowatt-hour (kWh) – Energy consumed by 1 kilowatt of power over 1 hour. The standard unit for electricity billing worldwide. 1 kWh = 3.6 MJ = 3,600,000 J exactly.

BTU (British Thermal Unit) – Energy needed to heat 1 pound of water by 1°F. Used for heating, cooling, and fuel content in the US. 1 BTU ≈ 1,055 J. Air conditioners are rated in BTU/hour.

Electronvolt (eV) – The energy gained by an electron accelerating through a potential difference of 1 volt. 1 eV = 1.602×10⁻¹⁹ J. Used in atomic, nuclear, and particle physics for its convenient scale.

Therm – Natural gas billing unit equal to 100,000 BTU ≈ 105.5 MJ. Used by gas utilities, especially in the US and UK.

Learn More

Explore our in-depth guides on this topic:

Énergie

About Energy Conversion

Common Energy Conversions

Energy Unit Reference

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