Energy Unit Converter

This calculator converts between the most common energy units: joules (J), kilojoules (kJ), calories (cal), kilocalories (kcal), watt-hours (Wh), kilowatt-hours (kWh) and electronvolts (eV).

Conversion factors

The main equivalences are:

• 1 kcal = 4,184 J
• 1 kWh = 3,600,000 J = 3.6 MJ
• 1 cal = 4.184 J
• 1 Wh = 3,600 J
• 1 eV = 1.602 × 10⁻¹⁹ J
• 1 BTU = 1,055.06 J

All conversions are performed by first converting to joules as the intermediate unit.

Example 1: calories to joules

Problem: Convert 500 kcal to joules.

1. Calculation:
   • 500 × 4,184 = 2,092,000 J = 2,092 kJ.

Answer: 500 kcal = 2,092,000 J = 2,092 kJ.

Example 2: kWh to calories

Problem: Convert 1 kWh to kcal.

1. Calculation:
   • 1 kWh = 3,600,000 J.
   • 3,600,000 / 4,184 ≈ 860.4 kcal.

Answer: 1 kWh ≈ 860.4 kcal.

Common uses of energy conversion

• Converting food calories to joules for scientific calculations.
• Comparing electrical consumption (kWh) with thermal energy.
• Computing food energy content in different units.
• Working with energy efficiency data.
• Converting units in physics and thermodynamics problems.
• Analyzing the energy content of fuels.

Common mistakes with energy units

• Confusing calories (cal) with kilocalories (kcal or "Cal" in nutrition).
• Not distinguishing between watts (power) and watt-hours (energy).
• Using approximate conversion factors when precision is needed.
• Forgetting that 1 Cal (nutrition) = 1 kcal = 1,000 cal.

Pro tip

In nutrition, when "calories" are mentioned they actually mean kilocalories. A 95-"calorie" apple actually has 95 kcal = 397,480 J. This confusion is very common.