Lightning distance calculator
This lightning distance calculator is a practical tool that estimates how far away a lightning strike occurred based on the time difference between seeing the lightning flash and hearing the thunder.
Storm distance:
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Related calculators:
What is lightning distance?
Lightning distance refers to the distance between the observer and the point where lightning strikes. Understanding this distance is crucial for both safety and scientific analysis.
How to estimate lightning distance (Flash-to-bang method)
This is the most practical and widely used method:
Step-by-step:
- See the flash of lightning.
- Count the seconds until you hear the thunder (the “bang”).
- Divide the seconds by:
- 3 for kilometers
- 5 for miles
Rule of thumb:
Sound travels ~343 meters per second (or 1,125 ft/sec) in dry air at 20°C (68°F).
Example:
If you count 10 seconds between flash and thunder:
Distance ≈ 10 ÷ 3 = ~3.3 km (or 2 miles)
Temperature’s role in lightning distance
The speed of sound in air is not constant—it varies with temperature. Since lightning distance is often estimated using the time it takes for thunder to reach you, the speed of sound directly affects the accuracy of that distance.
The physics behind it
The speed of sound in air increases as temperature increases.
The approximate formula for the speed of sound (v) in dry air is:
v = 331 + 0.6 \times T
where:
- v = speed of sound in meters per second (m/s)
- T = air temperature in °C
Example comparisons
| Temperature (°C) | Speed of Sound (m/s) | Effect on Distance |
|---|---|---|
| 0°C | ~331 m/s | Sound travels slower → greater time delay |
| 20°C | ~343 m/s | Standard estimate |
| 35°C | ~352 m/s | Sound travels faster → shorter time delay |
If you’re using a fixed value for the speed of sound (e.g., 343 m/s), you’re assuming room temperature (~20°C). But in reality:
- On hot days, sound reaches you faster → actual lightning is farther than a standard estimate might suggest.
- On cold days, sound is slower → actual lightning is closer than you’d estimate without adjusting for temperature.