Energy Converter
Convert between joules, calories, kWh, BTU, and more.
Energy is measured in an unusually large number of units because different fields developed their own conventions: physicists use joules, nutritionists use kilocalories (food Calories), engineers use BTU or kWh, and particle physicists use electron volts. Converting accurately between them matters when comparing appliance efficiency, understanding food labels, analyzing electricity bills, or working in engineering and science.
Popular Energy Conversions
Standards Note: A Kilowatt-Hour Is Just Energy at a Larger Scale
NIST lists 1 watt-hour as 3,600 joules, so every kilowatt-hour on an electric bill is simply 3.6 megajoules written in a more practical unit.
Joules, Calories, and Kilowatt-Hours
The joule (J) is the SI unit of energy — the work done by a force of one newton acting over one meter. A calorie (lowercase 'c') is the energy needed to raise 1 gram of water by 1°C — approximately 4.184 joules. The Calorie printed on food labels is actually a kilocalorie (kcal), equal to 1,000 small calories or 4,184 joules. A kilowatt-hour (kWh), the unit used to measure electricity consumption, equals 3,600,000 joules or 3,600 kJ. A typical US household uses about 877 kWh per month (EIA, 2022).
Practical Energy References
A 100-watt light bulb running for one hour uses 0.1 kWh. A typical microwave oven (1,000 W) uses 0.25 kWh in 15 minutes. An electric vehicle typically consumes 25–40 kWh per 100 miles. Burning 1 liter of gasoline releases about 34.2 MJ (megajoules) of energy — equivalent to 9.5 kWh. A 2,000 Calorie/day diet provides about 8,368 kJ or 2.32 kWh of chemical energy per day. Put another way, a 100W light bulb consumes more electrical energy in a day than your body uses in metabolic energy.
| Unit | Equivalent |
|---|---|
| 1 calorie (small) | 4.184 J |
| 1 kcal (food Calorie) | 4,184 J / 4.184 kJ |
| 1 kWh | 3,600,000 J / 3,600 kJ |
| 1 BTU | 1,055 J / 0.293 Wh |
| 1 MJ (megajoule) | 277.8 Wh / 238.8 kcal |
| 1 eV (electron volt) | 1.602 × 10⁻¹⁹ J |
BTU and Heating/Cooling Applications
The British Thermal Unit (BTU) remains common in US HVAC, heating, and air conditioning equipment. One BTU is the energy needed to raise one pound of water by 1°F — approximately 1,055 joules. Air conditioner capacity is rated in BTU/hour (often expressed simply as BTU). A 12,000 BTU/hr unit (1 ton of cooling) can cool a room of about 450–550 sq ft. Central AC systems are typically rated at 2–5 tons (24,000–60,000 BTU/hr). Gas furnaces are rated in BTU/hr input; a 100,000 BTU/hr furnace at 95% efficiency delivers 95,000 BTU/hr of usable heat.
Joules, Food Calories, & Kilojoules - Unit Conversion With Heat Energy - Physics Problems | The Organic Chemistry Tutor
This video ties together joules, food Calories, and kilojoules, making it a strong fit for readers bouncing between physics, nutrition, and everyday energy labels.
Video source: The Organic Chemistry Tutor
Further Reading
Sources & References
- NIST — Units and Conversion Factors — Energy unit conversions (joules, BTU, kWh) from NIST.