Light from the lightning strike arrives to your eyes virtually instantaneously. But thunder is sound, and thus travels at 770 mph (about 5 seconds to travel a mile, or 3 seconds to travel a kilometre).
So, from the time you see the lightning until you see the thunder, count the number of seconds before you hear thunder. And then
divide by 3 (to measure distance in km)
or
divide by 5 (to measure distance in miles)
One problem is that often the sound of thunder that you hear doesn't go with the flash of lightning that you saw. It may go with a different flash. This is especially true if the lightning started high in the cloud, in which case the the thunder is closer than the formula suggests. Or if the storm is settled in (there are lightning strikes all around you). Where the formula works best is when there is a clear storm front where lightning strikes are happening.
So, from the time you see the lightning until you see the thunder, count the number of seconds before you hear thunder. And then
divide by 3 (to measure distance in km)
or
divide by 5 (to measure distance in miles)
One problem is that often the sound of thunder that you hear doesn't go with the flash of lightning that you saw. It may go with a different flash. This is especially true if the lightning started high in the cloud, in which case the the thunder is closer than the formula suggests. Or if the storm is settled in (there are lightning strikes all around you). Where the formula works best is when there is a clear storm front where lightning strikes are happening.
