Energy Converter
Convert between joules, calories, BTU, kilowatt-hours, and other energy units
Energy Conversion Formulas
Understanding Energy Units
Energy is the capacity to do work, and it comes in many forms—heat, electricity, motion, and chemical bonds. Different fields use different units: physicists use joules, nutritionists use kilocalories (food Calories), HVAC engineers use BTU, and electric utilities use kilowatt-hours. Understanding these conversions is essential for comparing energy sources, calculating efficiency, and managing consumption.
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. Kilowatt-hours (kWh) measure electrical energy consumption—what appears on your electric bill. Calories measure heat energy, with the 'food Calorie' actually being a kilocalorie (1000 small calories).
This converter handles all common energy units from tiny electron-volts used in atomic physics to massive BTUs used in heating systems, making it useful for scientists, engineers, nutritionists, and homeowners alike.
Energy Unit Categories
Scientific (Joules)
SI unit of energy. 1 J = 1 kg·m²/s². Basis for all other energy conversions.
Nutritional (kcal)
Food energy. 1 food Calorie = 1 kcal = 4,184 J. Daily intake: 2000-2500 kcal.
Electrical (kWh)
Utility billing unit. 1 kWh = 3.6 MJ. Average US home uses 900 kWh/month.
Thermal (BTU)
HVAC and heating. 1 BTU heats 1 lb water by 1°F. = 1,055 J.
Energy Conversion Reference
| From | To | Multiply By | Application |
|---|---|---|---|
| Kilocalories | Kilojoules | 4.184 | Nutrition labels |
| kWh | BTU | 3,412 | HVAC efficiency |
| BTU | Joules | 1,055.06 | Heating calcs |
| Calories (small) | Joules | 4.184 | Chemistry |
| Foot-pounds | Joules | 1.356 | Mechanical work |
| Watt-hours | Joules | 3,600 | Batteries |
Practical Applications
Food Labels
US uses Calories (kcal), EU uses kilojoules. 1 Calorie = 4.184 kJ. A 500 Cal meal = 2,092 kJ.
Home Energy
Electric bill shows kWh. A 60W bulb for 10 hours = 0.6 kWh. At $0.12/kWh = $0.07.
AC/Heating
AC units rated in BTU/hour. 12,000 BTU/hr = 1 ton of cooling. Bigger isn't always better.
Battery Capacity
Batteries rated in Wh or mAh. Convert mAh to Wh: (mAh × voltage) ÷ 1000.
Frequently Asked Questions
What's the difference between calories and Calories?
A small calorie (cal) heats 1 gram of water by 1°C. A food Calorie (Cal, capital C) equals 1 kilocalorie (1000 small calories). Nutrition labels use Calories (kcal), though they often just write 'calories' lowercase.
How do I convert my electric bill to other units?
Your bill shows kWh. Multiply by 3,412 for BTU, by 3.6 for megajoules, or by 860 for kilocalories. A 1,000 kWh bill = 3.41 million BTU = 3,600 MJ.
Why do different countries use different energy units on food labels?
The US uses Calories (kcal), while the EU requires kilojoules (kJ) and may also show kcal. This is part of metric vs. imperial differences. International products often show both: '200 kcal (838 kJ)'.
How much energy does a human need per day?
Average adult needs 2,000-2,500 kcal/day (8,400-10,500 kJ). This equals about 2.4-3 kWh of energy—enough to power a 100W light bulb for 24-30 hours.
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