- 1). Choose how you want to count the seconds between the lightning and thunder. Count slowly, or use a clock, timer or stopwatch.
- 2). Use the "flash to bang method." First, stand safely back from a window and observe the lightning. Then count the number of seconds before you hear the rolls of thunder.
- 3). Divide the number of seconds by five to get the mileage distance. For example, if you hear thunder 15 seconds after a flash, divide 15 seconds by five, which equals three miles, an estimate of how far away the lightning is.