Lightning Distance Calculator
Calculate lightning distance instantly in your browser — the published formula, worked locally with no data sent anywhere.
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What this tool does
Calculate lightning distance instantly in your browser — the published formula, worked locally with no data sent anywhere. Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
How to use the Lightning Distance Calculator
- Enter or select seconds between the flash and the thunder.
- Enter or select air temperature (°c, adjusts the speed of sound).
- Read the calculated result; change any measurement to compare alternatives.
Formula
distance = seconds × speed of sound, where the speed of sound in air ≈ 331.3 + 0.606 × T(°C) m/s. Light arrives essentially instantly, so the delay is all sound travel time — the classic 'divide the seconds by 5 for miles, by 3 for kilometres' rule.
- seconds
- Seconds between the flash and the thunder
- temp
- Air temperature (°C, adjusts the speed of sound)
Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
Worked example
For lightning distance calculator, the following measurements illustrate the exact method: Seconds between the flash and the thunder: 5; Air temperature (°C, adjusts the speed of sound): 20.
Inputs
- Seconds between the flash and the thunder5
- Air temperature (°C, adjusts the speed of sound)20
Result
- Distance (miles)1.07
- Distance (km)1.72
- Distance (feet)5,633.53
- Speed of sound used (m/s)343.42
- Safety guidanceWithin 6 miles — seek proper shelter now; wait 30 minutes after the last thunder
Results explained
- Distance (miles)
- Distance (miles) from the formula above. Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
- Distance (km)
- Distance (km) from the formula above. Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
- Distance (feet)
- Distance (feet) from the formula above. Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
- Speed of sound used (m/s)
- Speed of sound used (m/s) from the formula above. Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
- Safety guidance
- Safety guidance from the formula above. Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
Frequently asked questions
distance = seconds × speed of sound, where the speed of sound in air ≈ 331.3 + 0.606 × T(°C) m/s. Light arrives essentially instantly, so the delay is all sound travel time — the classic 'divide the seconds by 5 for miles, by 3 for kilometres' rule.
Assumes sound travels in a straight line at a uniform temperature. Wind and temperature layers bend sound, so distant thunder can be inaudible even for nearby storms — never rely on silence as proof of safety.
Sound covers a mile in about 4.7 seconds at typical temperatures, which the classic rule rounds to 5. This calculator uses the exact temperature-adjusted speed instead of the rounded rule.
Every field is labelled with its unit — enter values in exactly the labelled unit and read the result in the labelled output unit. Fields with a unit symbol also support the site-wide imperial/metric switch, which converts before the formula runs.
It uses double-precision arithmetic and the published constants and formulas named on this page. The last displayed digit may be rounded, and real conditions can differ from the idealized model described in the assumptions.
Yes. Every calculation runs entirely in your browser; nothing you enter is uploaded, stored or shared.