Energy Converter
Convert energy units instantly — joules, calories, kilowatt-hours, BTU, electronvolts, and more. Use our free energy converter for physics, nutrition, and engineering needs.
Understanding Energy
Energy represents the capacity to do work or produce heat. Energy exists in many forms — kinetic (motion), potential (stored), thermal (heat), chemical (bonds), electrical, and nuclear. You use energy constantly — moving your body, powering devices, heating your home.
The joule (J) serves as the SI unit for energy, named after James Prescott Joule. One joule equals the work done by a one-newton force moving an object one meter. Calories measure food energy, kilowatt-hours measure electricity, and BTUs measure heating/cooling capacity.
Energy Formulas
Kinetic Energy
KE = ½ × m × v²
Mass times velocity squared, divided by 2
Example: 10 kg at 5 m/s = 125 J
Potential Energy (Gravity)
PE = m × g × h
Mass × gravity × height
Example: 10 kg × 9.81 × 2m = 196.2 J
Thermal Energy
Q = m × c × ΔT
Mass × specific heat × temperature change
Example: 1 kg water, 10°C rise = 41,840 J
Electrical Energy
E = P × t
Power × time
Example: 100W × 3600s = 360,000 J = 0.1 kWh
Mass-Energy Equivalence
E = m × c²
Einstein's equation: mass × speed of light squared
1 kg = 90,000,000,000,000,000 J
Work-Energy Theorem
W = F × d
Work equals force times distance
Example: 10 N × 5 m = 50 J
Energy Conversion Formulas
Joules to Calories
cal = J × 0.239006
Example: 100 J × 0.239006 = 23.9 cal
Calories to Joules
J = cal × 4.184
Example: 100 cal × 4.184 = 418.4 J
Kilowatt-hours to Joules
J = kWh × 3,600,000
Example: 1 kWh × 3,600,000 = 3.6 MJ
Joules to Kilowatt-hours
kWh = J ÷ 3,600,000
Example: 1,000,000 J ÷ 3,600,000 = 0.278 kWh
BTU to Joules
J = BTU × 1,055.06
Example: 10 BTU × 1,055.06 = 10,551 J
Joules to BTU
BTU = J × 0.000947817
Example: 10,000 J × 0.000947817 = 9.48 BTU
Common Energy Conversions
| Joules | Kilojoules | Calories | Watt-hours | BTU |
|---|---|---|---|---|
| 1 J | 0.001 kJ | 0.239 cal | 0.000278 Wh | 0.000948 BTU |
| 1,000 J | 1 kJ | 239 cal | 0.278 Wh | 0.948 BTU |
| 4,184 J | 4.184 kJ | 1,000 cal | 1.162 Wh | 3.966 BTU |
| 3,600 J | 3.6 kJ | 860 cal | 1 Wh | 3.412 BTU |
| 1,055 J | 1.055 kJ | 252 cal | 0.293 Wh | 1 BTU |
| 1 kWh | 3,600 kJ | 860,421 cal | 1,000 Wh | 3,412 BTU |
Energy Unit Reference Table
| Unit | Symbol | Equals 1 Unit In Joules | Primary Use |
|---|---|---|---|
| Joule | J | 1 J | SI unit, physics, engineering |
| Kilojoule | kJ | 1,000 J | Food labels (some countries), science |
| Calorie | cal | 4.184 J | Chemistry, small energy amounts |
| Kilocalorie (Food Calorie) | Cal, kcal | 4,184 J | Nutrition, food energy |
| Watt-hour | Wh | 3,600 J | Electrical energy, batteries |
| Kilowatt-hour | kWh | 3,600,000 J | Electricity billing, home energy |
| BTU | BTU | 1,055.06 J | HVAC, heating, natural gas (US) |
| Electronvolt | eV | 1.602×10⁻¹⁹ J | Atomic physics, particle physics |
Real-World Energy Examples
| Object/Activity | Joules | Calories | Description |
|---|---|---|---|
| Lifting an apple 1 meter | 1 J | 0.24 cal | Small mechanical work |
| Food calorie (1 Cal) | 4,184 J | 1,000 cal | Nutritional energy |
| AA battery | 10,000 J | 2,390 cal | Typical capacity |
| Smartphone battery | 54,000 J | 12,900 cal | 15 Wh battery |
| Daily food intake | 8,400,000 J | 2,000 Cal | Average adult |
| Gasoline (1 liter) | 34,000,000 J | 8,126,000 cal | Chemical energy |
| Household electricity (1 kWh) | 3,600,000 J | 860,421 cal | Energy unit billing |
Food Energy Content
| Food Item | Calories (Cal) | Kilojoules (kJ) |
|---|---|---|
| Apple (medium) | 95 Cal | 397 kJ |
| Banana (medium) | 105 Cal | 439 kJ |
| Bread (1 slice) | 79 Cal | 330 kJ |
| Egg (large) | 78 Cal | 326 kJ |
| Rice (1 cup cooked) | 205 Cal | 858 kJ |
| Chicken breast (100g) | 165 Cal | 690 kJ |
| Chocolate bar (50g) | 270 Cal | 1,130 kJ |
When to Use Each Energy Unit
Physics & Science
All scientific calculations, research, education
Engineering
Mechanical, electrical, thermal calculations
Nutrition
Food labels (Australia, Europe use kJ)
Nutrition
Food labels, diet tracking (US, many countries)
Exercise
Calories burned, fitness tracking
Chemistry
Reaction energies (small calories)
Electricity
Utility billing, home energy consumption
Batteries
EV battery capacity, home storage
Appliances
Energy ratings, consumption estimates
HVAC
Air conditioner, heater capacity ratings (US)
Natural Gas
Gas energy content, billing (US)
Industrial
Boilers, furnaces, process heating
Frequently Asked Questions
What is the difference between calories and Calories?
One Calorie (capital C, also written kcal) equals 1,000 calories (lowercase c). Food labels use Calories (kcal). One food Calorie equals 4,184 joules. When people say "calories" in nutrition, they mean kilocalories.
How many joules are in a kilowatt-hour?
One kilowatt-hour equals exactly 3,600,000 joules (3.6 megajoules). This represents one kilowatt of power used for one hour. Electricity bills charge per kWh consumed.
What is a BTU?
BTU stands for British Thermal Unit. One BTU raises one pound of water by one degree Fahrenheit. Air conditioners and heaters use BTU/h ratings. A typical window AC unit produces 5,000-12,000 BTU/h.
How do I convert food calories to joules?
Multiply food Calories (kcal) by 4,184. Example: 250 Cal × 4,184 = 1,046,000 J = 1,046 kJ. For small calories, multiply by 4.184 instead.
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