TFT

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

Core Energy Equations

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

Core Conversion Equations

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

JoulesKilojoulesCaloriesWatt-hoursBTU
1 J0.001 kJ0.239 cal0.000278 Wh0.000948 BTU
1,000 J1 kJ239 cal0.278 Wh0.948 BTU
4,184 J4.184 kJ1,000 cal1.162 Wh3.966 BTU
3,600 J3.6 kJ860 cal1 Wh3.412 BTU
1,055 J1.055 kJ252 cal0.293 Wh1 BTU
1 kWh3,600 kJ860,421 cal1,000 Wh3,412 BTU

Energy Unit Reference Table

UnitSymbolEquals 1 Unit In JoulesPrimary Use
JouleJ1 JSI unit, physics, engineering
KilojoulekJ1,000 JFood labels (some countries), science
Caloriecal4.184 JChemistry, small energy amounts
Kilocalorie (Food Calorie)Cal, kcal4,184 JNutrition, food energy
Watt-hourWh3,600 JElectrical energy, batteries
Kilowatt-hourkWh3,600,000 JElectricity billing, home energy
BTUBTU1,055.06 JHVAC, heating, natural gas (US)
ElectronvolteV1.602×10⁻¹⁹ JAtomic physics, particle physics

Real-World Energy Examples

Object/ActivityJoulesCaloriesDescription
Lifting an apple 1 meter1 J0.24 calSmall mechanical work
Food calorie (1 Cal)4,184 J1,000 calNutritional energy
AA battery10,000 J2,390 calTypical capacity
Smartphone battery54,000 J12,900 cal15 Wh battery
Daily food intake8,400,000 J2,000 CalAverage adult
Gasoline (1 liter)34,000,000 J8,126,000 calChemical energy
Household electricity (1 kWh)3,600,000 J860,421 calEnergy unit billing

Food Energy Content

Food ItemCalories (Cal)Kilojoules (kJ)
Apple (medium)95 Cal397 kJ
Banana (medium)105 Cal439 kJ
Bread (1 slice)79 Cal330 kJ
Egg (large)78 Cal326 kJ
Rice (1 cup cooked)205 Cal858 kJ
Chicken breast (100g)165 Cal690 kJ
Chocolate bar (50g)270 Cal1,130 kJ

When to Use Each Energy Unit

Joules (J) / Kilojoules (kJ)

Physics & Science

All scientific calculations, research, education

Engineering

Mechanical, electrical, thermal calculations

Nutrition

Food labels (Australia, Europe use kJ)

Calories (Cal/kcal)

Nutrition

Food labels, diet tracking (US, many countries)

Exercise

Calories burned, fitness tracking

Chemistry

Reaction energies (small calories)

Kilowatt-hours (kWh)

Electricity

Utility billing, home energy consumption

Batteries

EV battery capacity, home storage

Appliances

Energy ratings, consumption estimates

BTU

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.

Other Free Tools

Power Converter

Convert power units — watts, kilowatts, horsepower, megawatts, and more. Accurate online power converter for engineering calculations.

Pressure Converter

Convert pressure units — pascals, bar, PSI, atmospheres, torr, and more. Free online pressure converter for engineering and science.

Force Converter

Convert force units — newtons, pound-force, kilogram-force, dynes, and more. Free online force converter for physics and engineering.

Temperature Converter

Convert temperatures between Celsius, Fahrenheit, Kelvin, and Rankine. Free online temperature converter for weather, cooking, and science.

Acceleration Converter

Convert acceleration units — m/s², g-force, ft/s², Gal, and more. Accurate online converter for physics, aerospace, and mechanical engineering.

Specific Heat Capacity Converter

Convert specific heat capacity units — J/(kg·K), BTU/(lb·°F), cal/(g·°C), and more. Accurate online converter for thermodynamics and chemistry.

Heat Density Converter

Convert heat density units — J/m³, BTU/ft³, cal/cm³, and more. Free online converter for combustion engineering and fuel analysis.

Heat Flux Density Converter

Convert heat flux density units — W/m², BTU/(h·ft²), cal/(s·cm²), and more. Free online converter for thermal engineering and solar energy.

Thermal Conductivity Converter

Convert thermal conductivity units — W/(m·K), BTU/(h·ft·°F), cal/(s·cm·°C), and more. Free online converter for insulation and heat transfer engineering.

Thermal Resistance Converter

Convert thermal resistance units — K/W, °C/W, °F·h/BTU, and more. Accurate online converter for HVAC, insulation, and electronics cooling.

Radiation Dose Converter

Convert radiation dose units — gray, rad, sievert, rem, and more. Free online radiation dose converter for medical physics, radiology, nuclear safety, and health physics.

Radioactivity Converter

Convert radioactivity units — becquerels, curies, millicuries, rutherfords, and more. Free online radioactivity converter for nuclear medicine, radiation safety, and physics.

Radiation Exposure Dose Converter

Convert radiation exposure dose units — roentgens, coulombs/kg, milliroentgens, and more. Free online exposure dose converter for radiology, health physics, and radiation protection.

Speed Converter

Convert speed units — km/h, mph, m/s, knots, and more. Free online speed converter for travel, sports, physics, and engineering.

Weight and Mass Converter

Convert weight and mass units — kilograms, pounds, grams, ounces, tons, and more. Accurate online weight converter for cooking, shipping, and science.

Length Converter

Convert length units instantly — meters, feet, inches, kilometers, miles, yards, and more. Free online length converter for everyday and scientific use.

Volume Converter

Convert volume units — liters, gallons, milliliters, cubic feet, fluid ounces, and more. Free online volume converter for cooking and engineering.

Moment of Force Converter

Convert moment of force units — N·m, lbf·ft, kgf·m, and more. Free online bending moment converter for structural and mechanical engineering.

Torque Converter

Convert torque units — newton-meters, pound-feet, kilogram-force centimeters, and more. Accurate online converter for automotive and mechanical engineering.

Heat Transfer Coefficient Converter

Convert heat transfer coefficient units — W/(m²·K), BTU/(h·ft²·°F), and more. Accurate online converter for convection and HVAC engineering.

Time Converter

Convert time units — seconds, minutes, hours, days, weeks, months, years. Simple online time converter for everyday and scientific use.

Area Converter

Convert area units — square meters, acres, hectares, square feet, square kilometers, and more. Ideal for real estate and construction.

Calorie Burn Rate Calculator

Estimate calories burned per hour for running, cycling, swimming, walking, and more. Free online calorie burn rate converter based on activity type and body weight.

Horsepower to Animals Converter

How many horses is your car's engine worth? Convert horsepower to fun animal equivalents — horses, hamsters, elephants, and more. A lighthearted power converter for curious minds.

Electric Potential Converter

Convert electric potential and voltage units — volts, millivolts, kilovolts, megavolts, and more. Free online voltage converter for electronics and power systems.

Electric Field Strength Converter

Convert electric field strength units — V/m, kV/m, N/C, and more. Free online electric field converter for electrostatics and antenna design.

Frequency Converter

Convert frequency units — hertz, kilohertz, megahertz, gigahertz, RPM, and more. Free online frequency converter for electronics and audio engineering.

Wavelength Converter

Convert wavelength units across the electromagnetic spectrum — nanometers, micrometers, angstroms, and more. Free online converter for optics and physics.

Sound Pressure Converter — Pa to dB

Convert sound pressure between pascals and decibels (dB SPL) instantly. Free online sound pressure converter for acoustics, audio engineering, and noise measurement.

Thermal Expansion Converter

Convert thermal expansion coefficients — per Kelvin, per Celsius, per Fahrenheit, and more. Free online converter for materials science and engineering.