Energy Converter
Our free conversions & measurement calculator solves energy problems. Get worked examples, visual aids, and downloadable results.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Energy Converter
Calculator
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Formula: 1 cal = 4.184 J | 1 kWh = 3,600,000 J | 1 BTU = 1055.06 J | 1 eV = 1.602e-19 J
Worked example — 1 kWh = 3,600,000 J = 860,421 cal = 3,412.14 BTU
Formula
1 cal = 4.184 J | 1 kWh = 3,600,000 J | 1 BTU = 1055.06 J | 1 eV = 1.602e-19 J
The joule (J) is the SI unit of energy, defined as the work done when a force of one newton moves an object one meter. All other energy units convert to joules through a fixed, internationally agreed factor: calories via the mechanical equivalent of heat, kilowatt-hours via power multiplied by time, BTU via the heat needed to warm one pound of water by one degree Fahrenheit, and electronvolts via the charge of a single electron.
Worked Examples
Example 1: Electricity Bill Energy Use
Problem:A household appliance uses 1 kWh of electricity. Express this in joules, calories, and BTU.
Solution:Joules = 1 kWh x 3,600,000 J/kWh = 3,600,000 J Calories = 3,600,000 / 4.184 = 860,421 cal BTU = 3,600,000 / 1055.06 = 3,412.14 BTU
Result:1 kWh = 3,600,000 J = 860,421 cal = 3,412.14 BTU
Example 2: Food Energy to Joules
Problem:A snack bar contains 180 food Calories (kcal). Convert this to joules and kilojoules.
Solution:Joules = 180 kcal x 4184 J/kcal = 753,120 J Kilojoules = 753,120 / 1000 = 753.12 kJ
Result:180 Calories = 753,120 J = 753.12 kJ
Example 3: Particle Physics Energy Scale
Problem:A particle accelerator imparts 2.5 MeV of kinetic energy to an electron. Convert this to joules.
Solution:1 MeV = 1,000,000 eV x 1.602e-19 J/eV = 1.602e-13 J 2.5 MeV = 2.5 x 1.602e-13 = 4.005e-13 J
Result:2.5 MeV = 4.005 x 10^-13 joules
Frequently Asked Questions
What is the difference between a calorie and a kilocalorie?
A kilocalorie (kcal) equals 1000 small calories. Food labels use kilocalories but call them 'Calories' (capital C). One food Calorie equals 4184 joules. This distinction matters when converting energy in nutritional or scientific contexts. A food label stating '200 Calories' per serving is stating 200 kilocalories, or 836,800 joules — a common point of confusion for anyone reading labels from countries that list kilojoules explicitly.
How are joules related to kilowatt-hours?
One kilowatt-hour (kWh), the unit on electricity bills, equals 3,600,000 joules. This comes from 1000 watts multiplied by 3600 seconds in an hour. A 100-watt bulb running for 10 hours consumes 1 kWh or 3.6 million joules of energy. Utility companies bill in kWh rather than joules purely for convenience — a typical US household uses around 30 kWh (108 million joules) per day, a figure that would look unwieldy expressed only in joules.
How much energy is in common everyday activities and foods?
Concrete reference points make energy units easier to grasp: a slice of bread contains roughly 65 food Calories (272,000 joules); climbing a flight of stairs uses about 5,000 joules; a smartphone battery stores roughly 40,000 joules (11 Wh); a car battery stores about 1.8 million joules (0.5 kWh); and boiling a kettle of water uses approximately 400,000-500,000 joules. Comparing an unfamiliar energy quantity to one of these references is often faster than relying on unit conversion alone.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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