What is the width of a lightning bolt? I’ve read a lot about lightning, but I have never seen anything about its thickness.
—Al Kell, Chicago
The primary current- carrying portion of a lightning discharge isn’t even a half-inch across. The “return stroke”—the intense pulse that returns to the cloud from the ground—puts out most of the light that we see and does most of the damage associated with lightning. It may grow to a half-centimeter to centimeter in diameter (a centimeter is equivalent to 0.39 inch). This happens after the “stepped leader” drops earthward from the thunderhead and makes contact with the ground.
A wider charge field—up to six miles across—can cause hair to stand on end, but it is not part of the lightning bolt.