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Lightning Distance Calculator

Find how far away lightning is and your safety zone

Distance

2.1 mi

Km

3.4 km

Safety

Danger

Lightning Distance

2.1 miles

3.4 km

Safety Zone

Danger

Storm ETA

5 min

Danger

Seek shelter immediately. Lightning can strike within a 6-mile radius of the last thunder.

Details

Distance11289 ft / 3441 m
Sound Speed344 m/s
Storm Arrival (at 25 mph)5 min

Example Calculations

110 seconds delay at 70°F

Inputs

Delay10 seconds
Temperature70°F

Result

Distance2.1 miles

Sound speed at 70°F = 344.5 m/s. 10 × 344.5 = 3,445 m = 2.14 miles. DANGER zone—seek shelter.

225 seconds delay at 85°F

Inputs

Delay25 seconds
Temperature85°F

Result

Distance5.4 miles

Sound speed at 85°F = 349 m/s. 25 × 349 = 8,725 m = 5.4 miles. Still in danger zone—head for shelter.

Frequently Asked Questions

Q

How do you calculate lightning distance from thunder?

Count the seconds between the lightning flash and thunder, then divide by 5 for miles or by 3 for kilometers. Light travels instantly; sound travels about 1,125 ft/sec (343 m/s), so a 10-second delay means roughly 2 miles.

  • 1 second = ~1,125 feet
  • 5 seconds ≈ 1 mile
  • 3 seconds ≈ 1 kilometer
  • Sound speed varies with temperature
SecondsMilesKilometersSafety
5 sec1.0 mi1.6 kmDANGER
15 sec3.0 mi4.8 kmDANGER
30 sec6.0 mi9.7 kmWarning
60 sec12.0 mi19.3 kmAlert
Q

At what distance is lightning dangerous?

Lightning can strike up to 10–15 miles from the storm center (sometimes called "bolts from the blue"). The NWS 30-30 rule says: if the flash-to-thunder time is under 30 seconds (6 miles), seek shelter immediately.

  • Under 6 miles: seek shelter NOW
  • 6–10 miles: move toward shelter
  • 10–15 miles: be aware, have a plan
  • Wait 30 min after last thunder to resume
Q

Does temperature affect the calculation?

Yes. Sound speed depends on air temperature: 331.3 + 0.606 × T(°C) meters per second. At 32°F (0°C), sound travels 1,087 ft/sec. At 90°F (32°C), it is 1,152 ft/sec—a 6% difference.

  • Cold air: slower sound, underestimates distance
  • Hot air: faster sound, slightly further
  • Difference is ~6% across typical weather range
  • The 5-second rule is accurate enough for safety
Q

How fast does a thunderstorm approach?

Typical thunderstorms move at 25–35 mph. A storm 10 miles away could reach you in 15–25 minutes. Fast-moving squall lines can travel 50–60 mph, arriving in under 10 minutes from the same distance.

  • Average storm speed: 25–35 mph
  • 10 miles away: 15–25 min to arrival
  • Fast squall lines: 50–60 mph
  • Always seek shelter before the storm arrives

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Last Updated: Mar 20, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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