Science & Engineering
Thunder Distance Calculator
How far away is that lightning? Count the seconds.
Sound travels ~343 m/s; light is effectively instant. Multiply seconds between flash and thunder by 343 to get the distance to the strike.
Distance to Lightning
1.72 km
- meters
- 1715 m
- miles
- 1.07 miles
- safety
- Within strike range — seek shelter
Formula and method
Distance = Seconds × 343 m/s
Speed of sound at 20C in dry air.
Worked examples
5 seconds
- Seconds Between Flash and Boom:
- 5
Distance to Lightning: 1.72 km
Assumptions and limits
- Sea level, 20C
This tool provides an educational estimate. Rules, rates and personal circumstances can change the answer. Review the assumptions before relying on a result. Report a correction.
Common mistakes to avoid
- Using 5 seconds = 1 mile (only true approximately).
Frequently asked questions
When is lightning dangerous?
Within 10 km — go inside immediately.
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