How much energy is packed into that?
Energy density is why aviation still burns kerosene and why batteries are heavy. The numbers are not close.
Almost exactly a petrol
46 MJ is more than 5 of the 9 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| lead-acid battery | 0.144 MJ | 319× | |
| lithium-ion battery | 0.9 MJ | 51.1× | About 250 Wh/kg |
| wood | 16 MJ | 2.88× | |
| coal | 24 MJ | 1.92× | |
| ethanol | 26.8 MJ | 1.72× | |
| petrol | 46 MJ | 1× | |
| natural gas | 53.6 MJ | 0.858× | |
| hydrogen | 142 MJ | 0.324× | Per kilogram — but very hard to store |
| uranium-235 | 82,000,000 MJ | 1/1,782,609 | Fission |
Worth knowing
- Petrol carries about 50 times the energy per kilogram of a lithium-ion battery. Electric motors recover roughly a quarter of that gap in efficiency.
- Uranium fission releases about two million times the energy per kilogram of petrol, which is why a reactor refuels every 18 months.
Frequently asked
Why are electric cars still practical if batteries are so poor?
Because an electric drivetrain converts 85–90% of stored energy into motion against a petrol engine’s 25–30%. That closes a fiftyfold gap to about fifteenfold — enough for cars, not yet for aircraft.
Is hydrogen a good fuel?
By mass, the best chemical fuel there is. By volume it is terrible — even liquefied it holds a quarter of petrol’s energy per litre, and it must be kept at −253 °C.