What is the base unit of energy?

The SI base unit of energy is the joule (J). This converter uses joule as the internal reference and converts to kJ, cal, kcal, BTU, Wh, kWh, and therm.

How many joules are in 1 calorie?

1 small calorie (cal) = 4.184 joules. 1 kilocalorie (kcal, sometimes written Calorie in nutrition) = 4184 joules.

What is the difference between calorie and kilocalorie?

A nutrition label 'Calories' is actually kilocalories. 1 kcal = 1000 cal = 4184 J.

Energy & Heat Conversions – J, kJ, cal, kcal, BTU, kWh

Energy & Heat Conversions

Convert between the most common energy and heat units: joule (J), kilojoule (kJ), calorie (cal), kilocalorie (kcal), BTU (IT), watt-hour (Wh), kilowatt-hour (kWh), and therm (US). Ideal for engineering, HVAC, physics homework, cooking and energy reports.

Value

From

1000 J → 1.0000 kJ

Result

1.0000

Reference table

Unit	Symbol	To joule (J)	Notes
Joule	J	1	SI base unit
Kilojoule	kJ	1000	1 kJ = 1000 J
Calorie (small)	cal	4.184	Thermochemical
Kilocalorie	kcal	4184	Food “Calorie”
BTU (IT)	BTU	1055.05585262	HVAC, heating
Watt-hour	Wh	3600	Power × time
Kilowatt-hour	kWh	3,600,000	Utility bills
Therm (US)	thm	105,480,400	Natural gas billing

Formulas

General method: first convert to joules, then from joules to the target unit.

\( \text{J} = \text{value} \times \text{factor\_to\_joule(from)} \)

\( \text{target} = \text{J} \div \text{factor\_to\_joule(to)} \)

Examples

1) Convert 2 kWh to kJ:

2 kWh × 3,600,000 J/kWh = 7,200,000 J → ÷1000 = 7200 kJ

2) Convert 500 cal to BTU:

500 × 4.184 = 2092 J → 2092 ÷ 1055.05585262 ≈ 1.983 BTU

Energy vs heat

In thermodynamics, heat is energy in transit due to temperature difference. Here we treat them both as energy quantities and let you jump between common engineering and cooking units.