Using thunder to determine the distance to a strike

When you see the flash, count the seconds until you hear the thunder. Divide the seconds by five (5), and that will be the distance in miles to the strike. For instance, thunder heard 10 seconds after the lightning means the lightning struck 2 miles away.

Use the online distance calculator to do the math for you.

However, this method doesn't always tell the whole story about the lightning flash you just saw. For instance, most cloud-to-ground lightning flashes consist of long in-cloud branches that extend outward. So, if lightning strikes the ground 5 miles away, you may hear thunder directly above you after five seconds, meaning that the branches are one mile away (straight upwards), not the actual main bolt. (See diagram below)