How to Use the Lightning Distance Calculator
The flash of lightning reaches your eyes almost instantly, but the sound of thunder travels much slower — about 1,125 feet per second. Using that speed difference, the delay between seeing a flash and hearing the thunder tells you roughly how far away the strike hit. Multiply the delay in seconds by 1,125 to get feet, then divide by 5,280 to convert to miles.
This is the same idea behind the well-known "flash to bang" rule that some people use to estimate storm distance. A shorter delay means the strike happened closer to you, so if you're outdoors, treat any lightning as a signal to head inside right away.
Keep in mind the speed of sound shifts slightly with temperature and humidity, so this is an approximation for quick reference. Even if thunder is hard to hear, seeing lightning at all is a sign to move to a safe, enclosed space immediately.
Frequently Asked Questions
Light reaches you almost instantly, but sound travels much slower, at about 1,125 feet per second. Multiplying the delay between seeing the flash and hearing the thunder by the speed of sound gives you the approximate distance to the strike.
Not necessarily. Thunder can be hard to hear from farther away, and lightning can strike surprisingly far from the storm's core. If you see lightning or hear thunder at all, move indoors right away.