How large is a bolt of lightning?

          In a fraction of a millisecond, a bolt of lightning can discharge an electrical current of about 20,000 amps, with a field intensity of 200,000 volts per meter. Initial discharges, known as leaders, create a channel along which air molecules are ionized. Lightning channels can change direction several times, which is how the characteristic zigzag pattern of the main discharge is formed. Between thunderclouds and the Earth's surface, bolts of lightning reach an average length of between 1 and 2 km. Between clouds, the discharge can extend for distances of up to 7 km. In some cases, lightning has been known to travel up to 140 km.