Flash to bang estimates distance to a thunderstorm as one mile for every how many seconds?

• A. 3 seconds
• B. 4 seconds
• C. 5 seconds
• D. 6 seconds

Answer: (C)

The concept here is using the speed of sound to estimate how far away a thunderstorm is by timing the delay between lightning and thunder. Sound travels about 343 meters per second (roughly 1,125 feet per second), which is about 0.21 miles per second. That translates to roughly 4.7 seconds per mile. In practice, the common rule of thumb is five seconds per mile. So if you see lightning and hear thunder five seconds later, the storm is about one mile away. Temperature and humidity can tweak the speed a bit, but five seconds per mile is the standard quick estimate you’ll use. The other options would correspond to shorter or longer distances (about 0.6 miles for three seconds, ~0.8 miles for four seconds, ~1.2 miles for six seconds).