BTU (British Thermal Unit) is the energy needed to raise 1 pound of water by 1°F. 1 BTU = 1,055.06 joules = 0.293 watt-hours. It is used mainly in HVAC and heating systems in the US.

Energy Converter — Convert Joules, kWh, Calories, BTU & More

Q: How many joules is 1 kilowatt-hour?

1 kilowatt-hour (kWh) = 3,600,000 joules (3.6 MJ). This is because 1 kWh = 1000W x 3600 seconds = 3,600,000 J.

Q: What is the difference between calorie and kilocalorie?

1 kilocalorie (kcal) = 1,000 calories (cal). Food nutrition labels use kcal — when a food label says 200 Calories (with capital C), it actually means 200 kcal = 200,000 cal.

Q: How many joules is 1 calorie?

1 calorie (cal) = 4.184 joules. 1 kilocalorie (kcal) = 4,184 joules. This is the amount of heat needed to raise 1 gram of water by 1°C.

Q: How many kJ in 1 kWh?

1 kWh = 3,600 kilojoules (kJ). Formula: 1 kWh = 1000W x 3600s = 3,600,000 J = 3,600 kJ.

Q: What is an electronvolt?

An electronvolt (eV) is the energy gained by an electron moving through 1 volt of electric potential. 1 eV = 1.60218 x 10^-19 joules. It is used in particle physics and quantum mechanics.

What is Energy and Why Do We Convert It?

Energy is the capacity to do work — it exists in many forms including heat, light, electrical, chemical, and mechanical energy. The challenge is that different industries use completely different units. Scientists use joules, electricity companies bill in kilowatt-hours, nutritionists measure food in kilocalories, and HVAC engineers work in BTU. Converting between these units is essential in physics, engineering, nutrition, and energy management.

Energy Unit Conversion Formulas

kilojoule (kJ) = 1,000 joules (J)

kilowatt-hour (kWh) = 3,600,000 J = 3,600 kJ

calorie (cal) = 4.184 J

kilocalorie (kcal) = 4,184 J = 4.184 kJ

BTU = 1,055.06 J = 0.293 Wh

watt-hour (Wh) = 3,600 J

electronvolt (eV) = 1.60218 × 10⁻¹⁹ J

Energy Units — Reference Chart

Unit	Symbol	Equals in Joules	Common Use
Joule	J	1 J	Science, SI standard
Kilojoule	kJ	1,000 J	Food energy, chemistry
Kilowatt-hour	kWh	3,600,000 J	Electricity billing
Watt-hour	Wh	3,600 J	Battery capacity, small systems
Calorie	cal	4.184 J	Chemistry, physics
Kilocalorie	kcal	4,184 J	Food nutrition, diet
BTU	BTU	1,055.06 J	HVAC, heating (US)
Electronvolt	eV	1.602 × 10⁻¹⁹ J	Particle physics
Erg	erg	10⁻⁷ J	CGS physics
Therm	therm	105,480,400 J	Natural gas billing (US)

Real World Examples of Energy Conversion

Electricity bill: 1 unit on your bill = 1 kWh = 3,600,000 J = 860 kcal
Food: A 100g chocolate bar ≈ 500 kcal = 2,092 kJ = 0.581 Wh
Exercise: Running 1 km burns approximately 60-70 kcal = 250-293 kJ
AC unit: 1-ton AC uses 3.517 kWh per hour = 12,661,200 J
Smartphone battery: Typical 4,000 mAh battery ≈ 15 Wh = 54,000 J
Boiling water: Boiling 1 litre of water needs ≈ 335 kJ = 80 kcal

Food Calories vs Scientific Calories

This is one of the most confusing energy conversions in daily life. When a food label says "200 Calories" (with capital C), it actually means 200 kilocalories (kcal) — not 200 small calories (cal). So:

Food label "200 Cal" = 200 kcal = 200,000 cal = 836,800 J = 836.8 kJ

The small calorie (cal) is used in chemistry and physics. The large calorie (kcal or Cal) is used in nutrition. Always check which unit is being used when reading energy labels.

Electricity Consumption — kWh Explained

Your electricity bill is calculated in kWh (kilowatt-hours) — commonly called "units" in India. Here is how energy consumption translates across units:

Appliance	Power	1 Hour Energy	In kJ
LED bulb	10 W	0.01 kWh = 36 kJ	36,000 J
Ceiling fan	75 W	0.075 kWh = 270 kJ	270,000 J
Refrigerator	150 W	0.15 kWh = 540 kJ	540,000 J
Electric geyser	2,000 W	2 kWh = 7,200 kJ	7,200,000 J
1-ton AC	3,517 W	3.517 kWh = 12,661 kJ	12,661,200 J

Frequently Asked Questions

How many joules is 1 kilowatt-hour?

1 kWh = 3,600,000 joules (3.6 MJ). This is because 1 kWh = 1,000 W × 3,600 seconds = 3,600,000 J.

What is the difference between calorie and kilocalorie?

1 kilocalorie (kcal) = 1,000 calories. Food nutrition labels use kcal — when a label says "200 Calories" it means 200 kcal = 200,000 cal = 836,800 J.

How many joules is 1 calorie?

1 calorie (cal) = 4.184 joules. 1 kilocalorie (kcal) = 4,184 joules. This is the heat needed to raise 1 gram of water by 1°C.

How many kJ in 1 kWh?

1 kWh = 3,600 kilojoules (kJ). Formula: 1 kWh = 1,000W × 3,600s = 3,600,000 J = 3,600 kJ.

What is a BTU?

BTU (British Thermal Unit) = energy to raise 1 pound of water by 1°F. 1 BTU = 1,055.06 J = 0.293 Wh. Used mainly in US HVAC and heating systems.

What is an electronvolt?

An electronvolt (eV) = energy gained by an electron moving through 1 volt. 1 eV = 1.60218 × 10⁻¹⁹ J. Used in particle physics and quantum mechanics.

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