An average bolt of lightning, striking from cloud to ground, contains roughly one billion (1,000,000,000) joules of energy. This is no small amount, enough to power a 60-watt lightbulb for six months plus a forgotten open door refrigerator for a day.

Gasoline has an energy density of about 45 megajoules per kilogram (MJ/kg). This means that a gallon of gas has about 300 megajoules, or an average lightning bolt has the energy equivalent of about 3.3 gallons.

The energy in lightning bolts varies a great deal. Since it is very difficult to know when and where a lightening bolt will strike, it is impractical to attempt measurements. The energy must be calculated based on observed phenomena, such as width, duration and estimating the energy necessary to cause observed damage.

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