Energy Units Guide — Joules, kWh, Calories, BTU
Energy is measured in many different units depending on the context — electricity bills use kWh, food uses Calories (kcal), physics uses Joules, and HVAC uses BTU. Here's a clear guide.
Joule (J) — The SI Unit
The fundamental unit of energy. 1 Joule = force of 1 Newton moving 1 meter. Small in everyday terms — lifting a 100g object 1 meter takes about 1 Joule.
Kilowatt-hour (kWh) — Electricity
Equal to 3,600,000 Joules. What your electricity meter measures. Running a 1000W (1kW) appliance for 1 hour uses 1 kWh. In India, average household electricity cost is ₹5–8 per kWh.
Calorie vs Kilocalorie — Food Energy
This causes constant confusion. A food "Calorie" (capital C) = 1 kilocalorie = 1,000 scientific calories. Your 2,000 Calorie daily diet is actually 2,000 kcal = 8,368,000 Joules.
BTU (British Thermal Unit) — HVAC
Equal to 1,055 Joules. Used for air conditioner and heater ratings in the US and sometimes in India. A 1-tonne AC is approximately 12,000 BTU/hour.
Energy Conversion Table
| Unit | Joules | kWh | kcal |
|---|---|---|---|
| 1 Joule | 1 | 0.000000278 | 0.000239 |
| 1 kWh | 3,600,000 | 1 | 860 |
| 1 kcal | 4,184 | 0.001163 | 1 |
| 1 BTU | 1,055 | 0.000293 | 0.252 |
⚡ Electricity tip: A typical Indian household uses 200–500 kWh per month. A single 5-star rated 1.5-tonne AC running 8 hours/day uses roughly 90–120 kWh/month.