Calorie to Joule Converter
Convert calories to joules with our free online energy converter.
Quick Answer
1 Calorie = 4.184 joules
Formula: Calorie × conversion factor = Joule
Use the calculator below for instant, accurate conversions.
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Calorie to Joule Calculator
How to Use the Calorie to Joule Calculator:
- Enter the value you want to convert in the 'From' field (Calorie).
- The converted value in Joule will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Energy category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Calorie to Joule: Step-by-Step Guide
Converting Calorie to Joule involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
J = cal × 4.184Example Calculation:
1 cal = 4.184 J
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
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and Standards
The Small Calorie (Thermochemical Calorie)
The small calorie (cal), also called the gram calorie or thermochemical calorie, is defined as:
1 cal = 4.184 joules (exactly)
This represents the energy required to raise the temperature of one gram of pure water by one degree Celsius (from 14.5°C to 15.5°C) at standard atmospheric pressure (101.325 kPa).
The Large Calorie (Kilocalorie)
The large Calorie (Cal with capital C), properly called the kilocalorie (kcal), is defined as:
1 Cal = 1 kcal = 1,000 cal = 4,184 joules = 4.184 kilojoules
This represents the energy required to raise one kilogram of water by one degree Celsius. Food labels universally use this unit but write it as "Calorie" or "calories" (often lowercase), causing widespread confusion.
Historical Calorie Definitions
Multiple calorie definitions existed historically, all slightly different:
- 15°C calorie (cal₁₅): Energy to raise 1 g water from 14.5°C to 15.5°C = 4.1855 J
- 20°C calorie (cal₂₀): Energy to raise 1 g water from 19.5°C to 20.5°C = 4.182 J
- Mean calorie (cal_mean): 1/100 of energy to raise 1 g water from 0°C to 100°C = 4.190 J
- International Table calorie (cal_IT): Exactly 4.1868 J (defined in 1956)
- Thermochemical calorie (cal_th): Exactly 4.184 J (most common today)
The thermochemical calorie (4.184 J) is now standard in most applications.
Modern SI Replacement
The calorie was officially replaced by the joule (J) as the SI unit of energy in 1948. However, nutrition labeling and food science continue using kilocalories (Calories) globally, creating a dual-system reality.
and Standards
SI Definition
The joule is the SI derived unit of energy, work, and heat, defined as:
1 joule = the energy transferred when a force of 1 newton acts through a distance of 1 meter
Mathematically:
- 1 J = 1 N·m (newton-meter)
- 1 J = 1 kg·m²/s² (SI base units)
- 1 J = 1 W·s (watt-second)
- 1 J = 1 Pa·m³ (pascal-cubic meter)
Multiple Equivalent Definitions
Mechanical work: 1 J = work done moving an object 1 meter against 1 newton force
Electrical energy: 1 J = energy dissipated passing 1 ampere through 1 ohm resistance for 1 second (1 J = 1 A² · Ω · s = 1 V · A · s)
Kinetic energy: 1 J = kinetic energy of a 2 kg mass moving at 1 m/s (KE = ½mv² = ½ × 2 × 1² = 1 J)
Gravitational potential energy: 1 J = energy to lift ~102 grams by 1 meter on Earth (PE = mgh = 0.102 kg × 9.8 m/s² × 1 m ≈ 1 J)
Thermal energy: 1 J ≈ 0.239 calories (energy to raise 0.239 grams of water by 1°C)
2019 SI Redefinition
The 2019 SI revision redefined the joule based on exact fundamental constants:
- Planck constant (h): Exactly 6.62607015 × 10⁻³⁴ J·s
- Speed of light (c): Exactly 299,792,458 m/s
- Caesium hyperfine frequency: Exactly 9,192,631,770 Hz
Since the joule is defined in terms of kilogram, meter, and second, and these are now defined via fundamental constants, the joule has absolute stability independent of physical artifacts.
Standard Multiples
Kilojoule (kJ): 1 kJ = 1,000 J
- Typical for food energy (1 food Calorie = 4.184 kJ)
- Small appliance energy consumption
Megajoule (MJ): 1 MJ = 1,000,000 J = 1,000 kJ
- Vehicle fuel energy (1 liter gasoline ≈ 32 MJ)
- Industrial processes, home daily energy use
Gigajoule (GJ): 1 GJ = 1,000,000,000 J = 1,000 MJ
- Large-scale energy systems
- Natural gas (1 cubic meter ≈ 38 MJ, 1 therm = 105.5 MJ)
Terajoule (TJ): 1 TJ = 10¹² J
- Power plant output (per day/month)
- National energy statistics
Note: The Calorie is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Joule belongs to the imperial/US customary system.
History of the Calorie and Joule
and Evolution
Early Thermal Theory (1770s-1820s)
Swedish physicist Johan Wilcke first used the term "calorie" in 1772 while studying the specific heat capacity of different substances. French chemist Antoine Lavoisier and mathematician Pierre-Simon Laplace developed early calorimetry techniques in the 1780s using ice calorimeters, though they didn't use the calorie unit.
French engineer Nicolas Clément formally defined the calorie in 1824 as the heat required to raise one kilogram of water by one degree Celsius (equivalent to the modern kilocalorie). This definition emerged from steam engine efficiency studies during the Industrial Revolution.
Refinement and Standardization (1840s-1890s)
French chemists Pierre-Antoine Favre and Johann Silbermann refined Clément's definition in the mid-19th century to the small calorie (one gram of water by one degree Celsius), making it more practical for laboratory thermochemistry measurements.
German physicist Julius von Mayer and British physicist James Prescott Joule established the mechanical equivalent of heat in the 1840s-1850s, showing that heat and mechanical work were forms of the same phenomenon—energy. Joule's experiments demonstrated that approximately 4.184 joules of mechanical work produced one calorie of heat.
By the 1880s, the calorie became fundamental to thermochemistry, with chemists using it to measure heats of combustion, reaction, and formation for thousands of compounds.
Nutrition Science Revolution (1890s-1910s)
American agricultural chemist Wilbur Olin Atwater pioneered the use of calories in nutrition science in the 1890s. Working at Wesleyan University and the USDA, Atwater:
- Built the first human respiration calorimeter in the United States (1892)
- Measured the caloric content of hundreds of foods
- Established the Atwater system: 4 kcal/gram for carbohydrates and proteins, 9 kcal/gram for fats, 7 kcal/gram for alcohol
- Published the first food composition tables with calorie values (1896)
Atwater used the kilocalorie (large Calorie) for practical reasons—food portions contain thousands of small calories. His system remains the foundation of modern nutrition labeling.
Global Nutrition Labeling (1960s-Present)
The United States mandated calorie labeling on packaged foods in 1990 through the Nutrition Labeling and Education Act (NLEA), with regulations taking effect in 1994. The European Union, Australia, Canada, and most other nations followed with similar requirements.
International standards bodies attempted to introduce joule-based labeling:
- EU regulations required joules (kJ) alongside Calories (kcal) starting in the 1990s
- Australian/New Zealand labels show both kJ (primary) and Cal (secondary)
- Most other nations continue using Calories (kcal) exclusively
Despite official SI adoption of the joule, the Calorie remains dominant in consumer nutrition worldwide due to decades of established practice.
and Evolution
The Mechanical Equivalent of Heat (1840s-1850s)
James Prescott Joule (1818-1889), an English brewer and amateur scientist, conducted groundbreaking experiments demonstrating that mechanical work and heat are equivalent.
Famous paddle-wheel experiment (1843-1850): Joule built apparatus where falling weights drove paddles that stirred water in an insulated container. He precisely measured:
- Mechanical work input (weight × distance fallen)
- Temperature rise of water
- Established ratio: ~772 foot-pounds of work = 1 BTU of heat
- Modern equivalent: 4.184 joules = 1 calorie
Joule's work was initially met with skepticism but eventually revolutionized thermodynamics by unifying heat and mechanical energy under the first law of thermodynamics (conservation of energy).
Lord Kelvin (William Thomson) and Rudolf Clausius incorporated Joule's findings into the foundation of thermodynamics in the 1850s-1860s.
Adoption as a Unit (1882)
The British Association for the Advancement of Science formally adopted "joule" as the unit of work at its 1882 meeting, honoring James Prescott Joule's contributions. The joule was defined as 10⁷ ergs (the CGS energy unit).
Early definition: 1 joule = 10⁷ erg = 10⁷ g·cm²/s²
This established the joule in the meter-kilogram-second (MKS) system, precursor to SI.
International System of Units (1960)
The 11th General Conference on Weights and Measures (CGPM) in 1960 established the International System of Units (SI), designating the joule as the official SI unit for energy, work, and heat.
Unified energy unit: The joule replaced multiple historical units:
- Calorie (thermochemistry, nutrition)
- Erg (CGS physics)
- Foot-pound (engineering)
- Watt-hour (electricity)
- BTU (heating/cooling)
Despite SI adoption, many of these units persist in specific contexts (food Calories, kWh for electricity billing, BTU for HVAC).
Modern Precision (1990s-2019)
1990 redefinition: Linked to the volt and ohm through quantum electrical standards (Josephson effect and quantum Hall effect), enabling unprecedented precision.
2019 SI revision: Redefined the joule via exact fundamental constants (Planck constant, speed of light), eliminating dependence on physical prototypes. This "New SI" provides ultimate stability—joule can be reproduced anywhere in the universe using only constants and measurement equipment.
Common Uses and Applications: calories vs joules
Explore the typical applications for both Calorie (imperial/US) and Joule (imperial/US) to understand their common contexts.
Common Uses for calories
Nutrition and Food Science
The kilocalorie (food Calorie) is the global standard for food energy labeling:
- Nutrition Facts labels: Required in US, EU, Canada, Australia, Japan, and most nations
- Calorie counting apps: MyFitnessPal, Lose It!, Cronometer use kcal
- Restaurant menus: Chain restaurants in many countries must display Calories
- Weight management: "3,500 Calorie deficit = 1 pound lost" rule (approximate)
- Dietary guidelines: USDA recommends 2,000 Cal/day reference (individual needs vary)
- Meal planning: Registered dietitians prescribe meal plans in kcal targets
The capital-C "Calorie" convention (Cal) distinguishes food calories from scientific small calories (cal), though lowercase "calorie" appears on many labels causing confusion.
Thermochemistry and Chemical Engineering
The small calorie (cal) remains common in chemistry despite SI joule adoption:
- Heat capacity measurements: Specific heat often expressed in cal/(g·°C)
- Enthalpy of reaction: ΔH values published in both kcal/mol and kJ/mol
- Bond energies: C-H bond ≈ 99 kcal/mol (414 kJ/mol), C-C bond ≈ 83 kcal/mol (347 kJ/mol)
- Calorimetry: Bomb calorimeters measure heat of combustion in cal or kcal
- Physical chemistry textbooks: Many retain calories alongside joules for historical continuity
Exercise Physiology and Sports Science
Calories (kcal) measure energy expenditure and athletic performance:
- VO₂ max testing: Maximum oxygen consumption converted to Cal/min
- Heart rate monitors: Estimate calorie burn from HR, age, weight, gender
- Fitness trackers: Apple Watch, Fitbit, Garmin display "active Calories" and "total Calories"
- Exercise equipment: Treadmills, ellipticals, rowing machines show estimated Calories burned
- Sports nutrition: Athletes track calorie intake to match training expenditure (3,000-8,000+ Cal/day for elite athletes)
Medicine and Clinical Nutrition
Healthcare providers use Calories for patient care:
- Enteral/parenteral nutrition: Hospital feeding formulas prescribed in kcal/day
- Malnutrition treatment: Refeeding protocols specify gradual kcal increases
- Obesity medicine: Weight loss interventions target 500-1,000 Cal/day deficits
- Diabetes management: Carbohydrate counting considers total caloric intake
- Critical care: ICU patients receive calculated kcal needs (25-30 kcal/kg body weight/day)
- Eating disorder treatment: Recovery meal plans gradually increase kcal to restore weight
Heating and Cooling Systems (Historical)
Before universal adoption of BTUs and watts, calories measured heating/cooling:
- Steam heating systems: Rated in thousands of kcal/hour (now watts or BTU/h)
- Refrigeration: Early systems rated in kcal/hour removed (now tons or watts)
- Industrial processes: Heat input/output in Mcal (megacalories = 1 million cal = 1,000 kcal)
When to Use joules
Physics and Science
The joule is the universal energy unit in scientific research:
Mechanics: Kinetic energy (KE = ½mv²), potential energy (PE = mgh), work (W = F·d)
Thermodynamics: Heat transfer, enthalpy, internal energy, entropy (S units: J/K)
Electromagnetism: Electrical energy (E = V·I·t), magnetic energy (E = ½LI²), capacitor energy (E = ½CV²)
Quantum mechanics: Energy levels in atoms/molecules (though electronvolts often preferred)
Relativity: Mass-energy equivalence E = mc² (in joules when using SI units)
Engineering Applications
Engineers use joules across all disciplines:
Mechanical engineering: Impact energy, spring energy (E = ½kx²), rotational energy (E = ½Iω²)
Civil engineering: Structural load energy, seismic energy absorption
Aerospace engineering: Rocket propulsion energy, orbital energy calculations
Chemical engineering: Heat of reaction, activation energy, process energy requirements
Materials science: Fracture energy, strain energy density
Electrical and Electronics
Joules quantify electrical energy consumption:
Power consumption: Energy (J) = Power (W) × Time (s)
- 100W light bulb for 1 hour = 100 × 3,600 = 360,000 J = 360 kJ
Battery capacity: Often listed in watt-hours (Wh), convert to joules by × 3,600
- 10 Wh battery = 10 × 3,600 = 36,000 J = 36 kJ
Capacitor energy: E = ½CV² (where C in farads, V in volts, E in joules)
Energy efficiency: Comparing joules input vs. joules output determines efficiency percentage
Nutrition and Food Science
Many countries mandate both kilojoules and Calories on nutrition labels:
Australia/New Zealand: Kilojoules (kJ) primary, Calories secondary
European Union: Often lists both kJ and kcal
Conversion: 1 food Calorie (kcal) = 4.184 kJ
Example: 500 kJ = 500 ÷ 4.184 ≈ 120 kcal (Calories)
Climate and Energy Policy
Joules (typically in TJ, PJ, EJ) measure large-scale energy:
National energy consumption: Reported in exajoules (EJ = 10¹⁸ J) annually
- World primary energy: ~600 EJ/year
- United States: ~100 EJ/year
Carbon footprint: kg CO₂ per GJ of energy source
Renewable energy: Solar irradiance (W/m² → J/m² over time)
Energy intensity: Economic output per joule consumed (GDP/GJ)
Sports and Exercise Science
Joules measure human energy expenditure:
Metabolic equivalent (MET): 1 MET = ~4.184 kJ/hour per kg body weight at rest
Cycling power meters: Measure work in kilojoules per ride
Weightlifting: Work = weight × height × 9.8 (in joules)
- Deadlift 100 kg to 1 meter height = 100 × 9.8 × 1 = 980 J
Running economy: Joules per meter traveled
Additional Unit Information
About Calorie (cal)
What is the difference between cal and kcal?
cal (small calorie) = 4.184 joules—the energy to raise 1 gram of water by 1°C. Used in scientific contexts (chemistry, physics).
kcal (kilocalorie) = 4,184 joules = 1,000 cal—the energy to raise 1 kilogram of water by 1°C. Used in nutrition as "Calorie" (capital C).
Food labels display kilocalories (kcal) but call them "Calories" or "calories," causing widespread confusion.
Why do food labels use "Calories" instead of "calories"?
Food labels show the kilocalorie (kcal), which should technically be written as "Calorie" with capital C or "kcal" to distinguish from the small calorie (cal). However, regulations and common usage often write "calories" (lowercase), relying on context (nutrition labeling) to indicate kilocalories.
Historical reason: When Wilbur Atwater introduced food calorie measurements in the 1890s, he used kilocalories because food portions contain thousands of small calories. The "Calorie" (capital C) convention emerged to distinguish the two.
How many calories do I need per day?
Estimated daily needs (kcal/day):
- Sedentary women: 1,600-2,000 Calories
- Active women: 2,000-2,400 Calories
- Sedentary men: 2,000-2,600 Calories
- Active men: 2,400-3,000 Calories
Factors affecting needs:
- Age (decreases ~10 Cal/day per year after age 30)
- Sex (men typically need more due to higher muscle mass)
- Height and weight (larger bodies need more energy)
- Activity level (exercise increases expenditure significantly)
- Muscle mass (muscle burns more calories at rest than fat)
Use the Mifflin-St Jeor equation for personalized estimates:
- Men: (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161
Then multiply by activity factor (1.2 for sedentary, 1.375 for light activity, 1.55 for moderate, 1.725 for very active, 1.9 for extremely active).
How many calories should I eat to lose weight?
Safe weight loss rate: 0.5-2 pounds per week
Calorie deficit needed:
- 500 Cal/day deficit → ~1 pound lost per week
- 1,000 Cal/day deficit → ~2 pounds lost per week
Minimum intake guidelines:
- Women: Don't go below 1,200 Calories/day without medical supervision
- Men: Don't go below 1,500 Calories/day without medical supervision
Why minimums matter: Very low-calorie diets risk nutrient deficiencies, muscle loss, metabolic slowdown, and difficulty sustaining weight loss.
Better approach: Calculate your Total Daily Energy Expenditure (TDEE), then eat 10-25% less while maintaining adequate protein (0.7-1g per pound body weight) and strength training to preserve muscle mass.
Are calories the same as kilojoules?
No, they are different units measuring the same thing (energy):
1 Calorie (kcal) = 4.184 kilojoules (kJ)
Conversion:
- kcal → kJ: multiply by 4.184
- kJ → kcal: divide by 4.184
Regional use:
- United States, Canada: Calories (kcal) exclusively
- Australia, New Zealand: kJ primary, Calories secondary
- European Union: Both required (kJ first in some countries)
- Most of world: Calories (kcal) dominant
Quick approximation: 1 kJ ≈ 0.24 kcal, or 1 kcal ≈ 4.2 kJ
Why was the calorie replaced by the joule?
The joule became the SI standard unit of energy in 1948 for several reasons:
- Coherence: Joule integrates perfectly with other SI units (1 J = 1 kg·m²/s²)
- Universality: Applies to all forms of energy (mechanical, electrical, thermal), not just heat
- Precision: Joule has an exact definition based on fundamental constants
- No ambiguity: Multiple calorie definitions existed (15°C, 20°C, mean, thermochemical, IT)
Despite official replacement, the calorie persists in nutrition because:
- Decades of established practice and consumer familiarity
- Food databases and recipes use Calories
- Changing would require massive re-education and relabeling costs
- The kilocalorie provides convenient numbers for food portions (100-500 range vs. 400,000-2,000,000 joules)
Do different foods have different calorie densities?
Yes, calorie density varies enormously:
Very low calorie density (0-50 Cal/100g):
- Non-starchy vegetables: lettuce 15 Cal/100g, cucumber 16 Cal/100g, celery 16 Cal/100g
- Fruits: watermelon 30 Cal/100g, strawberries 32 Cal/100g
Low calorie density (50-150 Cal/100g):
- Lean proteins: chicken breast 165 Cal/100g, cod 82 Cal/100g
- Legumes: lentils 116 Cal/100g cooked, black beans 132 Cal/100g cooked
Medium calorie density (150-400 Cal/100g):
- Whole grains: brown rice 123 Cal/100g cooked, whole wheat bread 247 Cal/100g
- Starchy vegetables: potatoes 77 Cal/100g, corn 96 Cal/100g
High calorie density (400-900 Cal/100g):
- Fats and oils: olive oil 884 Cal/100g, butter 717 Cal/100g
- Nuts and seeds: almonds 579 Cal/100g, peanut butter 588 Cal/100g
- Processed foods: potato chips 536 Cal/100g, chocolate 546 Cal/100g
Why fat has highest density: Fat provides 9 Cal/g vs. 4 Cal/g for carbs/protein, making fatty foods extremely calorie-dense.
Does "negative calorie" food exist?
No, truly negative-calorie foods do not exist. All foods provide calories, though some extremely low-calorie vegetables come close.
The myth: Foods like celery supposedly require more calories to digest than they provide.
The reality:
- Celery contains 16 Calories per 100g (about 6 Calories per large stalk)
- Digestion burns ~10-30% of calories consumed (thermic effect of food)
- Celery digestion might use ~2 Calories per stalk
- Net result: Still positive 4 Calories per stalk
Closest candidates (still positive net calories):
- Celery, cucumbers, lettuce, zucchini (very low but never negative)
- Ice water technically uses ~8 Calories per liter to warm (negligible effect)
Bottom line: Very low-calorie vegetables are excellent for weight loss due to high volume and fiber, but they still provide net positive calories.
How accurate are calorie counts on food labels?
FDA allows ±20% margin of error on nutrition labels in the United States. Similar tolerances exist in other countries.
Why inaccuracy occurs:
- Natural variation in food composition (seasonal, variety, growing conditions)
- Measurement methods (Atwater system uses averages, not exact values)
- Rounding rules (labels round to nearest 5 or 10 Calories)
- Fiber calories counted differently (2 Cal/g vs. 4 Cal/g for total carbs)
Studies show:
- Restaurant foods average 18% more calories than posted
- Packaged foods usually within ±10% of label
- "Low calorie" foods (<40 Cal/serving) often more accurate in absolute terms
Calorie counting app accuracy: Database entries vary widely; verified entries (e.g., from USDA) are most reliable, while user-submitted entries can be off by 50%+ in some cases.
What is a "calorie bomb calorimeter"?
A bomb calorimeter is a laboratory device that precisely measures the energy content of food and other materials by burning them completely in pure oxygen and measuring the heat released.
How it works:
- Sample placed in sealed steel "bomb" container filled with pure oxygen (30 atm pressure)
- Bomb submerged in precisely measured water
- Electrical ignition burns sample completely
- Temperature rise in surrounding water measured
- Calories calculated: Heat (cal) = water mass (g) × temp rise (°C) × water specific heat
Accuracy: Modern bomb calorimeters measure to ±0.1% precision.
Why important: Food calorie values originally came from bomb calorimetry. However, human digestion doesn't extract 100% of calories (fiber partly undigested, protein incompletely oxidized), so Atwater factors adjust bomb calorimetry values for physiological availability.
Can you burn calories without exercise?
Yes, your body burns calories constantly through:
1. Basal Metabolic Rate (BMR): 60-75% of daily calories
- Cellular metabolism, protein synthesis, breathing, circulation, brain function
- Example: 1,400-1,800 Cal/day for typical adults at complete rest
2. Non-Exercise Activity Thermogenesis (NEAT): 15-30% of daily calories
- Fidgeting, maintaining posture, daily movements, occupational activities
- Can vary by 350-600 Cal/day between individuals
- Standing burns 50 more Cal/hour than sitting
3. Thermic Effect of Food (TEF): 8-15% of calories consumed
- Energy used to digest, absorb, and process nutrients
- Protein has highest TEF (20-30%), then carbs (5-10%), then fat (0-3%)
4. Exercise: 5-15% of daily calories (for sedentary to moderately active people)
Example breakdown (2,000 Cal/day total expenditure):
- BMR: 1,400 Cal (70%)
- NEAT: 400 Cal (20%)
- TEF: 150 Cal (7.5%)
- Exercise: 50 Cal (2.5%)
Takeaway: Most calories burned come from just being alive, not exercise, though exercise remains crucial for health, fitness, and weight management.
About Joule (J)
How do I convert joules to calories?
Formula: calories = joules ÷ 4.184
Examples:
- 4,184 J = 1,000 small calories = 1 kcal (food Calorie)
- 100 J = 100 ÷ 4.184 ≈ 23.9 calories
- 1,000 J = 1,000 ÷ 4.184 ≈ 239 calories
For food Calories (kcal): joules ÷ 4,184 = kcal
- 418,400 J ÷ 4,184 = 100 kcal (food Calories)
How do I convert joules to kWh?
Formula: kWh = joules ÷ 3,600,000
Why 3,600,000?: 1 kWh = 1,000 watts × 3,600 seconds = 3,600,000 joules
Examples:
- 3,600,000 J = 1 kWh
- 1,800,000 J = 0.5 kWh
- 108,000,000 J = 30 kWh (typical home daily use)
How much energy is 1 joule?
Physical examples:
- Lifting 100 grams (small apple) 1 meter against Earth's gravity
- 1 watt of power for 1 second
- Kinetic energy of 2 kg mass moving at 1 m/s
- Energy to heat 0.24 grams of water by 1°C
Perspective: 1 joule is small—about the energy in a single heartbeat. Practical applications typically use kilojoules (kJ), megajoules (MJ), or kilowatt-hours (kWh).
What is the relationship between watts and joules?
Power (watts) = Energy (joules) ÷ Time (seconds)
Or equivalently: Energy (joules) = Power (watts) × Time (seconds)
Definition: 1 watt = 1 joule per second (W = J/s)
Examples:
- 100W light bulb for 10 seconds = 100 × 10 = 1,000 J = 1 kJ
- 1,000W microwave for 2 minutes = 1,000 × 120 = 120,000 J = 120 kJ
- 1W for 1 hour = 1 × 3,600 = 3,600 J = 3.6 kJ
Takeaway: Watts measure the rate of energy use; joules measure the total amount of energy.
Why do energy bills use kWh instead of joules?
Historical reasons: Kilowatt-hours (kWh) became standard for electricity billing before SI joule adoption (1960).
Convenient numbers: Home electricity typically measures 10-50 kWh/day, equivalent to 36-180 MJ/day. Using joules would require large numbers (millions).
Industry inertia: Billions of meters and billing systems use kWh; switching would require enormous infrastructure investment.
Conversion: 1 kWh = 3,600,000 J = 3.6 MJ
Both valid: kWh and MJ are both acceptable SI-compatible units for electrical energy.
How many joules are in a food Calorie?
1 food Calorie (capital C, kilocalorie) = 4,184 joules = 4.184 kilojoules
Important distinction:
- Small calorie (cal): 4.184 J
- Food Calorie (Cal, kcal): 4,184 J = 4.184 kJ
Examples:
- 100 Calorie snack = 418,400 J = 418.4 kJ
- 2,000 Calorie daily intake = 8,368,000 J = 8.368 MJ
- Banana (105 Calories) = 439,320 J ≈ 439 kJ
Labeling variation: Some countries (Australia, EU) show energy in both kJ and kcal.
What's the difference between joules and electronvolts?
Both measure energy but use vastly different scales:
Joule (J): SI unit for macroscopic energy (mechanical, thermal, electrical)
Electronvolt (eV): Atomic-scale energy unit (energy gained by electron crossing 1 volt)
Conversion: 1 eV = 1.602 × 10⁻¹⁹ J (extremely tiny in macroscopic terms)
Usage:
- Joules: Everyday physics, engineering, household energy
- Electronvolts: Atomic physics, chemistry, particle physics, semiconductors
Example: Visible light photon ≈ 2 eV ≈ 3.2 × 10⁻¹⁹ J
How do joules relate to kinetic energy?
Kinetic energy formula: KE = ½mv²
Where:
- m = mass (kg)
- v = velocity (m/s)
- KE = kinetic energy (joules)
Examples:
- 1 kg at 1 m/s: KE = ½ × 1 × 1² = 0.5 J
- 10 kg at 10 m/s: KE = ½ × 10 × 10² = 500 J
- 1,000 kg (small car) at 20 m/s (72 km/h): KE = ½ × 1,000 × 20² = 200,000 J = 200 kJ
- 70 kg person at 3 m/s (jogging): KE = ½ × 70 × 3² = 315 J
Note: Kinetic energy grows with velocity squared, so doubling speed quadruples energy.
Can you create or destroy joules?
No, energy (in joules) is conserved according to the first law of thermodynamics (conservation of energy).
Energy can only transform:
- Mechanical → thermal (friction converts motion to heat)
- Chemical → thermal (combustion releases heat)
- Electrical → mechanical (motors convert electricity to motion)
- Nuclear → thermal → mechanical → electrical (nuclear power plants)
Total joules remain constant in isolated systems, though energy may become less useful (second law: entropy increases).
Mass-energy equivalence: Einstein's E = mc² shows mass can convert to energy and vice versa, but total mass-energy (in joules) is conserved.
How many joules does a human use per day?
Basal metabolism (resting): ~7,000,000-9,000,000 J (7-9 MJ = 1,700-2,200 kcal)
Total daily energy expenditure (including activity):
- Sedentary: ~8,000,000-10,000,000 J (8-10 MJ = 2,000-2,400 kcal)
- Moderate activity: ~10,000,000-12,000,000 J (10-12 MJ = 2,400-3,000 kcal)
- Very active: ~12,000,000-16,000,000 J (12-16 MJ = 3,000-4,000 kcal)
- Elite athlete training: ~16,000,000-33,000,000 J (16-33 MJ = 4,000-8,000 kcal)
Energy sources: Carbohydrates (17 kJ/g), proteins (17 kJ/g), fats (37 kJ/g)
Efficiency: Human body ~20-25% efficient at converting food energy to mechanical work; rest becomes heat.
Conversion Table: Calorie to Joule
| Calorie (cal) | Joule (J) |
|---|---|
| 0.5 | 2.092 |
| 1 | 4.184 |
| 1.5 | 6.276 |
| 2 | 8.368 |
| 5 | 20.92 |
| 10 | 41.84 |
| 25 | 104.6 |
| 50 | 209.2 |
| 100 | 418.4 |
| 250 | 1,046 |
| 500 | 2,092 |
| 1,000 | 4,184 |
People Also Ask
How do I convert Calorie to Joule?
To convert Calorie to Joule, enter the value in Calorie in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our energy converter page to convert between other units in this category.
Learn more →What is the conversion factor from Calorie to Joule?
The conversion factor depends on the specific relationship between Calorie and Joule. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Joule back to Calorie?
Yes! You can easily convert Joule back to Calorie by using the swap button (⇌) in the calculator above, or by visiting our Joule to Calorie converter page. You can also explore other energy conversions on our category page.
Learn more →What are common uses for Calorie and Joule?
Calorie and Joule are both standard units used in energy measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our energy converter for more conversion options.
For more energy conversion questions, visit our FAQ page or explore our conversion guides.
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All Energy Conversions
Other Energy Units and Conversions
Explore other energy units and their conversion options:
- Kilojoule (kJ) • Calorie to Kilojoule
- Megajoule (MJ) • Calorie to Megajoule
- Gigajoule (GJ) • Calorie to Gigajoule
- Watt-hour (Wh) • Calorie to Watt-hour
- Kilowatt-hour (kWh) • Calorie to Kilowatt-hour
- Megawatt-hour (MWh) • Calorie to Megawatt-hour
- Kilocalorie (kcal) • Calorie to Kilocalorie
- British Thermal Unit (BTU) • Calorie to British Thermal Unit
- Therm (therm) • Calorie to Therm
- Foot-pound (ft⋅lb) • Calorie to Foot-pound
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Fundamental physical constants and unit conversions
Bureau International des Poids et Mesures — International System of Units (SI) definitions and standards
International Organization for Standardization — Quantities and units international standards series
Last verified: February 19, 2026