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Lightning Distance Calculator

Science & Engineering

Flash-to-thunder seconds to distance, safety rules

Quick Answer

Lightning Distance Calculator: Flash-to-thunder seconds to distance, safety rules. Distance = seconds × speed of sound; light is effectively instant.

s
°C
Storm distance
1.03 km
1030 m ≈ 0.64 mi
Within 10 km — seek shelter NOW (30-30 rule)

Calculation steps

  1. 1Speed of sound at 20°C: v = 331.4 + 0.6 × 20 = 343.4 m/s
  2. 2Light reaches you almost instantly (300,000 km/s); sound takes the measured seconds.
  3. 3Distance = 343.4 × 3 = 1030 m = 1.03 km
  4. 4Quick rule: seconds ÷ 3 ≈ km (at ~20°C).
Sound speed343.4 m/s
Distance1.03 km
Miles0.64 mi
SafetyDanger zone

Reference table (20°C)

SecondsDistanceRisk level
< 3 s< 1 kmExtreme — lightning can strike here
3–10 s1–3.5 kmHigh — stop outdoor activity
10–30 s3.5–10 kmModerate — seek shelter (30-30 rule)
> 30 s> 10 kmLower — still monitor the storm
The 30-30 rule: if flash-to-thunder is 30 seconds or less, go indoors immediately; wait 30 minutes after the last thunder before going back out. Sound speed rises ~0.6 m/s per °C, so winter storms sound slightly "closer" than the same distance in summer.

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How to Use

  1. Enter known quantities: fill values and confirm units in the Lightning Distance Calculator.
  2. Instant solution: unknowns solve live with the formula shown transparently.
  3. Use constant/material tables: standard physical constants and material data are listed on this page.
  4. Compare conditions: change inputs to compare scenarios.

Key Points

  • Lightning Distance Calculator is a free online science & engineering tool — open and use, no sign-up.
  • All calculations run locally in your browser; your data never leaves the device.
  • Key capability: Flash-to-thunder seconds to distance, safety rules.
  • Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

Flash-to-bang distance

Distance = seconds × speed of sound; light is effectively instant
Temperature-corrected sound: v = 331.3 × √(1 + T/273.15) m/s (≈343 m/s at 20°C)
Quick rule: seconds ÷ 3 ≈ km
30/30 safety rule: under 30s → go indoors; wait 30 min after the last thunder

Example: 6 seconds → ≈2.06 km — high risk, seek shelter now.

FAQ

How do I use the Lightning Distance Calculator?
Open the page and fill in the input fields — results update automatically. Flash-to-thunder seconds to distance, safety rules.
Are the results accurate?
Yes. Standard formulas and conversion factors are used and verified.
Is it free? Do I need to sign up?
Completely free. No registration, login or download required.
Does it work on mobile?
Yes. The responsive design works on phones, tablets and desktops.
Is my data saved?
No. Everything runs locally in your browser.

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Source & Updates

Based on CODATA recommended constants and standard physics formulas. Last updated: 2025-07

Last updated:

Formulas and content on this page are reviewed by the YiJianSuan team. For reference only — official sources prevail.

Maintained and periodically reviewed by the YiJianSuan editorial team — review process in ourEditorial Policy.

Cite this page: YiJianSuan. Lightning Distance Calculator[EB/OL]. https://www.yijiansuan.com/en/c/science/lightning

Results provided by this tool are for reference only and do not constitute professional advice.