A storm approaches; all of a sudden, you see lightning followed by a deafening roar of thunder. He looks close – too close. Calculating the distance of a lightning can serve to keep your peace of mind if you are in a safe place; but it can also help you know if you need to find that safe place as soon as possible. So how far were you from the radius? Read on to find out.

## Steps

### Method 1 of 1: Calculating the radius distance

#### Step 1. Look for a flash of lightning in the sky

#### Step 2. Count the number of seconds it takes to hear thunder

If you have a watch, start timing as soon as lightning strikes, and stop as soon as you hear thunder. If you don't have a watch, try to count the seconds yourself as accurately as possible. Say "one crocodile, two crocodile…" in your head as you count.

#### Step 3. Calculate the radius distance in miles or kilometers

Sound travels a mile every five seconds and a kilometer every three seconds. So if you want to know your distance from the radius, divide the number of seconds by 5 to get the answer in miles, and by 3 if you want the answer in kilometers. The difference between when you see lightning and when you hear thunder is because sound travels much slower than light. Understand what you did:

- Let's say you've counted 18 seconds. To find the radius distance in miles, divide 18 by 5; the result is 3, 6 miles. To find the lightning distance in kilometers, divide 18 by 3; the answer is six kilometers.
- While it's not possible to get a completely accurate result – as temperature and humidity slightly influence the speed of sound – this is a good way to calculate your distance from a lightning bolt.

#### Step 4. Calculate the distance of a ray in feet or meters

Sound travels at a speed of about 344 meters, or 1,129 feet, per second. To calculate radius distance in meters, round 344 to 340 and multiply the number of seconds by 340. To calculate radius distance in feet, round 1129 to 1130 and multiply the number of seconds by 1130. Here is an example:

### Let's say you've counted 3 seconds. Multiply this number by 340 to find the distance in meters: 3 x 340 = 1020 meters. Multiply this number by 1130 to find the distance in feet: 3 x 1130 = 3,390 feet

## Tips

- If there are frightened children around, find out the distance of the lightning and tell them. This will help alleviate their fear and they are likely to even ask, "How do you know this?"
- Spread this method to people. Many of them still believe in the myth that the number of seconds you count is equal to the number of kilometers away from the beam.
- Sound travels through the air at slightly different speeds depending on the temperature and relative humidity of the air. The difference is quite small, however, and will not substantially affect your calculations. For more information, consult the sound speed calculators found on the internet.
- Of course, there is a large margin of error in this method. If possible, calculate the distance of several thunders and average them for more accuracy.
- If you have a map and a compass, plot the location of each ray with a line on the map in the direction of the ray and a cross at the calculated distance along that line.
- This method can also be used to teach students to calculate distance, speed and time.
- If a lightning strike hits a point 1 mile (1.6 km) away, you will see the flash approximately 0.00000536 seconds after it occurs, and you will hear it approximately 4.72 seconds after the phenomenon. If you calculate the difference between these two experiments, you will find that you hear the lightning about 4.71999 seconds after it actually occurred. Therefore, 5 seconds per mile is a very reliable approximation.

## Notices

- Lightning can kill. It's a good idea to learn how to protect yourself during a storm.
- Due to the way sound travels and how different objects such as mountains and buildings interact with sound waves, this is not the most reliable way to calculate the distance of lightning. Don't let your life depend on it. Find out about local weather forecasts.
- If you discover that the lightning occurred less than a mile away, find shelter immediately. Lightning discharge can hit it.
- If you don't see the beam directly, the sound you heard might have been a reflection of a building or mountain, which increases the time between the two events (the flash and the bang); in this case, the lightning seems farther away than it actually is. Consider nearby objects and obstacles (especially large ones), as the sound should "double up" and bump into them. Any indirect path will be longer than the distance you are trying to calculate.
- This activity must not be done outdoors. If you're close enough to hear thunder, then you're close enough to be hit by lightning. Lightning travels very quickly, and people more than 10 miles away from the storm have been hit. If possible, seek shelter immediately.