How do I convert Kilocalorie to Kilojoule?

To convert Kilocalorie to Kilojoule, multiply the kcal value by 4.184. The formula is: kJ = kcal × 4.184. For example, 100 kcal = 100 × 4.184 = 418.4 kJ. This conversion is essential for understanding food energy content, where many countries show both Calories and kilojoules on food labels.

Energy Converter - Joule, Kilowatt-hour, Calorie & More Units

Complete Guide to Energy Conversion

Energy conversion is essential across physics, chemistry, nutrition, electrical engineering, thermal systems, mechanical engineering, and everyday measurements. Whether you're calculating food calories in kilocalories, converting electrical energy from kilowatt-hours to joules, analyzing thermal energy in BTU and therms, measuring mechanical energy in foot-pounds and newton-meters, working with atomic energy in electron-volts, converting between imperial and metric systems, or converting between different energy units, our free online energy converter makes it easy to convert between Joule, Kilowatt-hour, Calorie, BTU, Electron-volt, Foot-pound, and other energy units instantly. Understanding energy units and conversions is crucial for accurate measurements in physics, chemistry, nutrition, electrical engineering, thermal systems, and international communication.

Understanding Energy Measurement Systems

Energy is the capacity to do work or produce heat, measured in various units depending on the application. The International System of Units (SI) uses the Joule as the base unit, while different industries use specialized units like kilowatt-hours for electricity, calories for nutrition, BTU for heating, and electron-volts for atomic physics. Understanding these units and their conversions is essential for accurate measurements across scientific, engineering, and everyday applications.

SI Units (Scientific)

Joule (J) - The Base Unit

The Joule is the SI base unit for energy, named after English physicist James Prescott Joule. One Joule equals the energy transferred when a force of one Newton is applied over a distance of one meter (1 J = 1 N·m). In practical terms, one Joule is roughly the energy needed to lift a small apple (100 grams) one meter high against Earth's gravity. The Joule serves as the foundation for all other metric energy units, which use standard SI prefixes to create multiples and submultiples.

Joule Multiples

Kilojoule (kJ): 1,000 J - Common for food energy labels and scientific calculations
Megajoule (MJ): 1,000,000 J - Used for large energy measurements, daily energy intake
Gigajoule (GJ): 1,000,000,000 J - Used for very large energy measurements, industrial processes

Joule Submultiples

Millijoule (mJ): 0.001 J - Very small energy measurements
Microjoule (µJ): 0.000001 J - Extremely small energy measurements
Nanojoule (nJ): 0.000000001 J - Nanoscale energy measurements
Attojoule (aJ): 10⁻¹⁸ J - Atomic and subatomic energy measurements

Electrical Energy Units

Watt-second and Watt-hour

Watt-second (W·s) equals one Joule, representing energy from one watt of power for one second. Watt-hour (Wh) equals 3,600 Joules, representing energy from one watt of power for one hour. These units are commonly used for battery capacity in electronics and small devices.

Kilowatt-hour and Larger Units

Kilowatt-hour (kWh) equals 3,600,000 Joules (3.6 MJ), representing energy from one kilowatt of power for one hour. This is the standard unit for electrical energy consumption on utility bills. Megawatt-hour (MWh) equals 3.6 GJ, and Gigawatt-hour (GWh) equals 3.6 TJ, used for large-scale electrical energy measurements.

Kilowatt-second

Kilowatt-second (kW·s) equals 1,000 Joules, representing energy from one kilowatt of power for one second. Used for short-duration high-power energy measurements.

Food & Nutrition Units

Calorie (cal) - Small Unit

The calorie (lowercase, cal) is the energy needed to raise 1 gram of water by 1°C. The thermochemical calorie equals 4.184 Joules exactly. The IT calorie (International Table) equals 4.1868 Joules. Used in chemistry and scientific contexts.

Kilocalorie (kcal) - Food Calories

The kilocalorie (kcal) equals 1,000 calories or 4,184 Joules (thermochemical) or 4,186.8 Joules (IT). This is what food labels call "Calories" (uppercase C). A typical adult needs 2,000 kcal daily. The nutritional calorie equals 4,186.8 Joules.

Thermal Energy Units

BTU (British Thermal Unit)

BTU is the energy needed to raise 1 pound of water by 1°F. The IT BTU equals 1,055.05585262 Joules, while the thermochemical BTU equals 1,054.35026449 Joules. Common in US heating/cooling systems and natural gas measurements. Mega BTU (MBtu) equals 1,055,055,852.62 Joules.

Therm Units

Therm equals 100,000 BTU (IT) or 105,505,585.262 Joules. Therm (EC) equals 105,506,000 Joules, and Therm (US) equals 105,480,400 Joules. Used for natural gas energy measurements in the United States and Europe.

Mechanical Energy Units

Force-based Units

Newton-meter (N·m) equals one Joule, representing work done by a force. Kilogram-force meter equals 9.80665 Joules. Pound-force foot (ft·lbf) equals 1.3558179483314 Joules. These units are commonly used in mechanical engineering and torque measurements.

Horsepower Units

Horsepower hour (hp·h) equals 2,684,519.537696 Joules. Horsepower (metric) hour equals 2,647,795.5 Joules. Used for mechanical work and energy in engine and motor applications.

Explosives and Large Energy Units

Ton of Explosives

Ton (explosives) equals 4.184 gigajoules (4,184,000,000 Joules), representing the energy released by one ton of TNT. Kiloton equals 4.184 terajoules, Megaton equals 4.184 petajoules, and Gigaton equals 4.184 exajoules. Used for nuclear and explosive energy measurements.

Fuel Oil Equivalents

Fuel oil equivalent @kiloliter equals 40.19 gigajoules. Fuel oil equivalent @barrel (US) equals 6.386 gigajoules. Used for energy content comparisons in fuel and energy systems.

Atomic/Quantum Physics Units

Electron-volt

Electron-volt (eV) equals 1.602176634 × 10⁻¹⁹ Joules, representing the kinetic energy gained by an electron accelerated through one volt potential difference. Kiloelectron-volt (keV) equals 1.602176634 × 10⁻¹⁶ Joules, and Megaelectron-volt (MeV) equals 1.602176634 × 10⁻¹³ Joules. Used extensively in atomic, nuclear, and particle physics.

Hartree and Rydberg

Hartree energy equals 4.3597447222071 × 10⁻¹⁸ Joules, representing the atomic unit of energy. Rydberg constant equals 2.1798723611035 × 10⁻¹⁸ Joules, half of the Hartree energy. Used in quantum chemistry and atomic physics calculations.

CGS Units

Erg and Dyne-centimeter

Erg equals 10⁻⁷ Joules (0.0000001 J). Dyne-centimeter equals 10⁻⁷ Joules, same as erg. Used in the CGS (centimeter-gram-second) system for small energy measurements in physics and chemistry.

How to Convert Joule to Kilowatt-hour

Converting Joule to Kilowatt-hour is one of the most common energy conversions, especially in electrical engineering, utility billing, and energy consumption analysis. To convert from Joule to Kilowatt-hour, divide the Joule value by 3,600,000. This conversion factor comes from the definition: 1 kilowatt-hour = 1 kilowatt × 1 hour = 1,000 watts × 3,600 seconds = 3,600,000 Joules. For example, 3,600,000 J ÷ 3,600,000 = 1 kWh. This conversion is essential for understanding electrical energy consumption, where utility bills show energy in kilowatt-hours while scientific calculations often use Joules. The relationship is straightforward: simply divide Joules by 3,600,000 to get kilowatt-hours, or multiply kilowatt-hours by 3,600,000 to get Joules. For quick mental calculations, you can approximate 1 kWh ≈ 3.6 MJ, though our converter uses the exact conversion factor for precision. This conversion is particularly important when analyzing electricity bills, calculating energy costs, comparing electrical energy with other energy forms, and understanding battery capacity in watt-hours and kilowatt-hours.

Energy vs Power: Understanding the Relationship

One of the most important concepts in energy conversion is understanding the relationship between energy and power:

Power: The rate at which energy is transferred or converted, measured in Watts (Joules per second). Power represents how quickly energy is used or produced.
Energy: The total amount of work done or heat transferred, measured in Joules, kilowatt-hours, or other energy units. Energy represents the capacity to do work.

The relationship is: Energy = Power × Time, or E = P × t. For example, a 100-watt light bulb operating for 10 hours uses 100 W × 10 h = 1,000 Wh = 1 kWh = 3,600,000 J of energy. Understanding this distinction helps clarify that energy is the total amount, while power is the rate of energy transfer or conversion.

Energy Conversion Formulas

Our energy converter uses these precise formulas for accurate conversions:

Joule to Kilowatt-hour:

kWh = J ÷ 3,600,000

Kilowatt-hour to Joule:

J = kWh × 3,600,000

Joule to Calorie:

cal = J ÷ 4.184

Calorie to Joule:

J = cal × 4.184

Joule to Kilocalorie (food Calorie):

kcal (Cal) = J ÷ 4,184

Kilocalorie to Joule:

J = kcal × 4,184

BTU to Joule:

J = BTU × 1,055.05585262

Joule to BTU:

BTU = J ÷ 1,055.05585262

Electron-volt to Joule:

J = eV × 1.602176634 × 10⁻¹⁹

Joule to Electron-volt:

eV = J ÷ (1.602176634 × 10⁻¹⁹)

Foot-pound to Joule:

J = ft·lbf × 1.3558179483314

Joule to Foot-pound:

ft·lbf = J ÷ 1.3558179483314

Energy Formula:

E = P × t (where E is energy, P is power, t is time)

Energy Conversion Table

Quick reference for converting between common energy units:

Unit	Joules (J)	kWh	kcal (Cal)	BTU
1 J	1	2.78 × 10⁻⁷	0.000239	0.000948
1 kJ	1,000	0.000278	0.239	0.948
1 MJ	1,000,000	0.278	239	948
1 kWh	3,600,000	1	860.421	3,412
1 kcal	4,184	0.001163	1	3.966
1 BTU	1,055.06	0.000293	0.252	1
1 Wh	3,600	0.001	0.860	3.412
10 J	10	2.78 × 10⁻⁶	0.00239	0.00948
100 J	100	2.78 × 10⁻⁵	0.0239	0.0948
1,000 J	1,000	0.000278	0.239	0.948
10,000 J	10,000	0.00278	2.39	9.48
100,000 J	100,000	0.0278	23.9	94.8
1,000,000 J	1,000,000	0.278	239	948
10 kWh	36,000,000	10	8,604	34,120
100 kWh	360,000,000	100	86,040	341,200
1,000 kWh	3,600,000,000	1,000	860,400	3,412,000
100 kcal	418,400	0.1163	100	396.6
1,000 kcal	4,184,000	1.163	1,000	3,966
10,000 BTU	10,550,600	2.93	2,520	10,000
100,000 BTU	105,505,600	29.3	25,200	100,000
1 MWh	3,600,000,000	1,000	860,400	3,412,000
1 GWh	3,600,000,000,000	1,000,000	860,400,000	3,412,000,000
1 ft·lbf	1.356	3.77 × 10⁻⁷	0.000324	0.001285

Common Energy Conversion Examples

Electrical Energy (kWh to J, MJ):

1 kWh = 3.6 MJ = 3,600,000 J
10 kWh = 36 MJ = 36,000,000 J
100 kWh = 360 MJ = 360,000,000 J
1,000 kWh = 3.6 GJ = 3,600,000,000 J
0.1 kWh = 360 kJ = 360,000 J
50 kWh = 180 MJ = 180,000,000 J
1 MWh = 3.6 GJ = 3,600 MJ

Food Energy (kcal to kJ, MJ):

100 kcal = 418.4 kJ = 0.4184 MJ
250 kcal = 1,046 kJ = 1.046 MJ
500 kcal = 2,092 kJ = 2.092 MJ
1,000 kcal = 4,184 kJ = 4.184 MJ
2,000 kcal = 8,368 kJ = 8.368 MJ
1 g carbs = 4 kcal = 16.7 kJ
1 g fat = 9 kcal = 37.7 kJ

Thermal Energy (BTU to J, MJ):

1,000 BTU = 1.055 MJ = 1,055,000 J
10,000 BTU = 10.55 MJ = 10,550,000 J
100,000 BTU = 105.5 MJ = 105,500,000 J
1 BTU = 1,055 J = 0.252 kcal
5,000 BTU = 5.275 MJ = 5,275,000 J
1 MBtu = 1.055 GJ = 1,055,000,000 J

Mechanical Energy (ft·lbf to J):

1 ft·lbf = 1.356 J
10 ft·lbf = 13.56 J
100 ft·lbf = 135.6 J
1,000 ft·lbf = 1,356 J = 1.356 kJ
1 hp·h = 2,684,520 J = 2.685 MJ
1 N·m = 1 J

Frequently Asked Questions (FAQ)

How do I convert Joule to Kilowatt-hour?

To convert Joule to Kilowatt-hour, divide the J value by 3,600,000. The formula is: kWh = J ÷ 3,600,000. For example, 3,600,000 J = 3,600,000 ÷ 3,600,000 = 1 kWh. One Kilowatt-hour equals exactly 3,600,000 Joules by definition. This conversion is essential for understanding electrical energy consumption, where utility bills show energy in kilowatt-hours while scientific calculations often use Joules.

How many Joules are in 1 Kilowatt-hour?

One Kilowatt-hour equals exactly 3,600,000 Joules (3.6 megajoules). To convert kWh to J, multiply the kWh value by 3,600,000. For example, 10 kWh = 10 × 3,600,000 = 36,000,000 J = 36 MJ. This conversion is essential for understanding electrical energy consumption and utility bills.

How do I convert Joule to Calorie?

To convert Joule to Calorie, divide the J value by 4.184. The formula is: cal = J ÷ 4.184. For example, 100 J = 100 ÷ 4.184 = 23.9 calories. One calorie equals exactly 4.184 joules by definition. For food Calories (kilocalories), divide by 4,184: 1,000,000 J ÷ 4,184 = 239 kcal.

How do I convert Calorie to Joule?

To convert Calorie to Joule, multiply the cal value by 4.184. The formula is: J = cal × 4.184. For example, 100 cal = 100 × 4.184 = 418.4 J. For food Calories (kilocalories), multiply by 4,184: 100 kcal = 100 × 4,184 = 418,400 J = 418.4 kJ.

What is a Joule in simple terms?

A Joule is the SI unit of energy. It's the energy needed to apply a force of one Newton over a distance of one meter (1 J = 1 N·m). In practical terms, one Joule is roughly the energy needed to lift a small apple (100 grams) one meter high. It's named after English physicist James Prescott Joule.

How do I convert BTU to Joule?

To convert BTU to Joule, multiply the BTU value by 1,055.05585262. The formula is: J = BTU × 1,055.05585262. For example, 10 BTU = 10 × 1,055.05585262 = 10,550.5585262 J ≈ 10.55 kJ. BTU (British Thermal Unit) is commonly used in heating, cooling, and energy efficiency ratings in the United States.

What is the difference between calorie and Calorie (kilocalorie)?

A calorie (lowercase, cal) is a small unit equal to 4.184 joules. A Calorie (uppercase, Cal or kcal) is a kilocalorie, equal to 1,000 calories or 4,184 joules. Food labels use Calories (kcal) - what we call dietary calories. So 100 Calories in food = 100 kcal = 100,000 cal = 418,400 joules.

What is an Electron-volt and how does it convert to Joules?

An Electron-volt (eV) is a very small unit of energy used in atomic and particle physics. One electronvolt equals 1.602176634 × 10⁻¹⁹ Joules. To convert eV to J, multiply by 1.602176634 × 10⁻¹⁹. For example, 1 eV = 0.0000000000000000001602 J. It's the kinetic energy gained by an electron accelerated through one volt potential difference.

How do I convert Foot-pound to Joule?

To convert Foot-pound to Joule, multiply the ft·lbf value by 1.3558179483314. The formula is: J = ft·lbf × 1.3558179483314. For example, 100 ft·lbf = 100 × 1.3558179483314 = 135.58179483314 J ≈ 135.6 J. Foot-pound is commonly used for mechanical energy and torque measurements in the United States.

Can I use this energy converter for electricity bills?

Yes! This energy converter is perfect for understanding electricity consumption. Utility bills show energy in kWh (kilowatt hours). Convert kWh to Joules, megajoules, or other units to compare with other energy measurements. For example, 100 kWh = 360,000,000 J = 360 MJ = 86,040 kcal.

How do I convert Therm to Joule?

To convert Therm to Joule, multiply the therm value by 105,505,585.262. The formula is: J = therm × 105,505,585.262. For example, 1 therm = 1 × 105,505,585.262 = 105,505,585.262 J ≈ 105.5 MJ. Therm is commonly used for natural gas energy measurements in the United States.

What units are supported in this energy converter?

Our energy converter supports 60+ units including: Joule, Kilojoule, Megajoule, Gigajoule, Calorie, Kilocalorie, Kilowatt-hour, Megawatt-hour, Gigawatt-hour, Watt-hour, BTU, Therm, Horsepower hour, Electron-volt, Megaelectron-volt, Foot-pound, and many more. All conversions use precise conversion factors based on international standards.

How accurate is this energy converter?

Our energy converter uses precise conversion factors based on international standards. Results are calculated with high precision and automatically formatted for optimal readability. All conversions follow official SI unit definitions and internationally recognized energy unit relationships.

What are common energy values in everyday life?

Common energy values: Food (100-500 kcal per meal), Electricity (10-30 kWh per day for homes), Heating (10,000-100,000 BTU for HVAC systems), Battery (50-100 Wh for smartphones, 50-100 kWh for electric cars), Exercise (200-500 kcal per hour), Sunlight (1,000 W/m² = 3.6 MJ/m² per hour).

Real-World Applications

Nutrition and Food Science

Energy conversion is fundamental in nutrition for converting between dietary Calories (kilocalories) and Joules. Food labels in many countries now show both Calories and kilojoules (kJ). A 2,000 Calorie diet equals 8,368 kJ. Macronutrients provide different energy: carbohydrates and proteins provide 4 Calories/gram (17 kJ/g), while fats provide 9 Calories/gram (38 kJ/g). Converting between these units helps understand food energy content and dietary requirements.

Electrical Systems and Power Bills

Kilowatt hours (kWh) measure electrical energy consumption. Understanding kWh helps manage electricity usage and costs. A typical US home uses 30 kWh/day (108 MJ). Common appliances: LED bulb (10W) uses 0.24 kWh/day, refrigerator uses 1-2 kWh/day, electric water heater uses 12 kWh/day. Converting to Joules helps compare electrical energy with other energy forms and understand energy consumption patterns.

Heating, Cooling, and HVAC

BTU ratings indicate heating or cooling capacity. Air conditioners are rated in BTU/hour (e.g., 10,000 BTU/hr = 2.93 kW). Furnaces might be 80,000-100,000 BTU/hr (23-29 kW). Understanding BTU to Joule or kWh conversions helps compare different heating and cooling systems, calculate energy costs, and optimize HVAC efficiency.

Mechanical Engineering

Mechanical energy conversion is essential for understanding work, torque, and energy in mechanical systems. Converting between foot-pounds, newton-meters, and joules helps engineers work with international equipment, understand energy requirements, and design efficient mechanical systems.

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Tips for Energy Conversion

Quick Approximation: For Joules to food Calories, divide by 4,000 (exact: 4,184)
Remember Key Values: 1 kcal = 4.184 kJ, 1 kWh = 3.6 MJ, 1 BTU = 1,055 J, 1 ft·lbf = 1.356 J
Calorie Confusion: Food Calories (uppercase) are kilocalories—1,000× larger than scientific calories (lowercase)
Electricity Costs: Multiply kWh by your utility rate (e.g., $0.12/kWh) to calculate energy costs
Battery Capacity: Higher Wh or kWh ratings mean more energy storage and longer device runtime
Energy vs Power: Energy (J, kWh) is total amount, Power (W, kW) is rate of energy transfer
Common Conversions: 1 kWh ≈ 3.6 MJ, 1 kcal ≈ 4.2 kJ, 1 BTU ≈ 1 kJ, 1 eV ≈ 1.6 × 10⁻¹⁹ J