About Energy Units

The SI unit of energy is the joule (J). The calorie (cal) measures food energy — note that food "Calories" (kcal) are actually kilocalories, 1,000 times larger than a thermochemical calorie. The kilowatt-hour (kWh) is used for electricity billing. The BTU (British Thermal Unit) is common in HVAC and US energy contexts.

Common Conversions

  • 1 kWh = 3,600,000 J = 3,600 kJ
  • 1 kcal (food Cal) = 4,184 J
  • 1 BTU = 1,055 J
  • 1 kJ = 0.2778 Wh
  • 1 eV = 1.602 × 10⁻¹⁹ J

Everyday Energy Context

  • Typical daily food intake: 2,000–2,500 kcal
  • 100W bulb running 1 hour = 0.1 kWh
  • Boiling 1 L of water ≈ 0.1 kWh
  • Average Indian home uses ~90–100 kWh/month
  • 1 litre of petrol ≈ 34 MJ of chemical energy