Frequently Asked Questions — MJ/kg to kWh/kg
Question: How many kWh/kg is 1 MJ/kg?
Answer: 1 MJ/kg = 0.2777777778 kWh/kg. Since 1 kWh = 3.6 MJ, divide MJ/kg by 3.6 to get kWh/kg.
Question: How do I convert MJ/kg to kWh/kg?
Answer: Divide the value in MJ/kg by 3.6 (or multiply by 0.2778). For example, gasoline at 44 MJ/kg ÷ 3.6 ≈ 12.22 kWh/kg.
Question: What is the reverse conversion — kWh/kg to MJ/kg?
Answer: 1 kWh/kg = 3.6 MJ/kg. Multiply kWh/kg by 3.6 to get MJ/kg.
Question: Why is kWh/kg used for batteries?
Answer: kWh/kg (kilowatt-hour per kilogram) is the standard unit for battery energy density because it directly shows how much electrical energy a battery can store per unit of weight. Lithium-ion batteries typically achieve 0.1–0.3 kWh/kg (0.36–1.08 MJ/kg). Gasoline at 12.2 kWh/kg is still ~40× more energy-dense than Li-ion batteries.
Question: What are typical MJ/kg values for common fuels?
Answer: Hydrogen ≈ 142 MJ/kg (39.4 kWh/kg), natural gas ≈ 55 MJ/kg (15.3 kWh/kg), propane ≈ 50 MJ/kg (13.9 kWh/kg), gasoline ≈ 44 MJ/kg (12.2 kWh/kg), diesel ≈ 43 MJ/kg (11.9 kWh/kg), ethanol ≈ 27 MJ/kg (7.5 kWh/kg), coal ≈ 24–35 MJ/kg (6.7–9.7 kWh/kg).