# Nine seconds between the flash and the thunder. How far away was it?

Divide the seconds by **five** for miles, by **three** for kilometres: nine seconds is just under two miles. And the part that matters: if you can hear thunder, the storm is close enough to strike.

By Marius Comper · 24 September 2026 · every number comes from published studies; find them under [sources](#surse)

## How many seconds did you count?

Slow seconds pass between the flash and the thunder. Pick your number and see the circle on the map of your town.

**First, guess: you counted nine seconds. How far away was the lightning?**
One mile, Two miles, Nine miles.
Yes. Nine divided by five is just under two miles.

**Without an electronic counter, the rule is the same:**
- 5: one mile
- 15: three miles
- 30: six miles
- 45: nine miles

In Bucharest like anywhere else: lightning at fifteen seconds is three miles from you.

If you can hear thunder, you are already close enough for lightning to strike you. [Take shelter.](#adapost)

## Why you divide

You see the flash almost at once and hear the thunder much later. The delay is the time sound needs to cross the air to you.

Sound moves through air at 344 metres a second at 20 degrees and 331.5 metres a second at zero degrees. A kilometre takes it 2.91 seconds in summer and 3.02 seconds in winter. That is why the rule says three in kilometres and five in miles: exact in cold air, rounded a few per cent under the true distance in warm air.

The light doesn't keep you waiting. At 299,792,458 metres a second, it crosses three kilometres in 10 millionths of a second. What you count is only the sound's journey.

**Guess, then check yourself against the bars: the air around a stroke, against the surface of the Sun, is it hotter or colder?**
Hotter. Five times hotter.

## How hot is lightning?

Guess, then check yourself against the bars: the air around a stroke, against the surface of the Sun, is it hotter or colder?

The American service says the air around a stroke reaches 50,000 degrees Fahrenheit, which is 27,760 degrees Celsius. The surface of the Sun is about 5,500 degrees. Divide and you get five.

With one qualification the same service makes: lightning itself has no temperature, since it is a movement of electric charges. What heats up is the air it passes through.

When that heat hits a tree, the water in the wood turns to steam on the spot, and the tree can burst apart or lose a strip of bark.

## Where does most lightning fall?

Between 2010 and 2022, the instruments caught an average of 760,000 flashes a year over Romania. Most fall over the Southern Carpathians, fewest in the east and south-east.

Three quarters of the flashes fall between June and August, peaking in June with 32.5% of the year's total. Winter, December to February, brings 0.027%, too little to see on the chart. The storm season runs May to September, and the peak hour is the afternoon, around 15–16.

The busiest year measured was 2010, with about 1.1 million flashes. In an average year, high summer brings some 6,200 flashes a day.

Two yearly totals appear on this page: 440,000 and 760,000. That is no increase. The first counts only flashes that reach the ground, between 2003 and 2007 (2006 excepted). The second adds the ones between clouds, between 2010 and 2022. Different quantities, different periods.

- Most: maximum about 6.5 (Southern Carpathians)
- Much: over 4.5 (the west and the foothills)
- Middle: between 3 and 4.5
- Least: under 3 (the east and south-east)

## The lightning that comes back

The saying goes that lightning never strikes the same place twice. The instruments say otherwise: tall, lonely places are hit again and again.

The Empire State Building in New York is hit about 25 times a year, which is nearly once a fortnight.

An instrumented tower is no ordinary roof, and the number 25 says nothing about how often a house is hit. It only proves that repeat strikes happen.

## What to do when the storm starts

The American guidance below is quoted word for word; the Romanian rules that follow are translated from the IGSU flyer.

1. Immediately move to safe shelter: a substantial building with electricity or plumbing or an enclosed, metal-topped vehicle with windows up.
2. Stay in safe shelter at least 30 minutes after the last sound of thunder.
3. Stay off corded phones, computers and other electrical equipment.
4. Avoid plumbing, including sinks, baths and faucets.

**From Romania's Inspectorate for Emergency Situations (IGSU), in translation:**

1. Stop everything you are doing outdoors.
2. Go inside a house, a building or a car (though you may still be hurt if lightning hits the car, you are much better protected inside the vehicle than outside).
3. Close the windows and doors.
4. Unplug appliances and other electrical equipment.
5. Avoid tall objects: a tall tree standing alone in the open, fields, beaches or boats on the water, metal objects (farm machinery, poles, farm equipment, motorbikes, bicycles, and the like).
6. If you did not reach shelter and feel your hair stand on end, lightning may be about to strike. Crouch down, cover your ears and head, keep your heels together!
7. In a forest, shelter among the shorter trees.
8. In the open, move to low ground (a valley).
9. On a lake, reach the shore urgently and shelter at once.
10. In a group, keep at least 5 metres from other people.
11. Call 112 at once for anyone knocked unconscious by lightning!

Between 1999 and 2015, Romania recorded 724 lightning deaths, 42.6 a year on average. The yearly average fell from 65, between 1999 and 2003, to 23.2, between 2011 and 2015, but the rate remains one of the highest in Europe. Most victims, 78%, lived in rural areas.

## True or false: eight questions

Eight statements, each proven by the page's sources. Answer, then pass your score on.

- **Lightning never strikes the same place twice.** False. It does. The Empire State Building is hit about 25 times a year. ([NOAA](https://www.noaa.gov/stories/5-striking-facts-versus-myths-about-lightning-you-should-know))
- **If you count 15 seconds to the thunder, the lightning was about three miles away.** True. 15 divided by 5 is 3, the guide's own example (about five kilometres). ([NOAA](https://www.noaa.gov/jetstream/lightning/lightning-safety))
- **The air around a stroke can get hotter than the surface of the Sun.** True. 50,000 degrees against 10,000: five times hotter. ([NWS](https://www.weather.gov/safety/lightning-temperature))
- **Three quarters of Romania's lightning falls in summer.** True. About 75% falls between June and August, peaking in June. ([Cristian et al. 2024](https://rrp.nipne.ro/2024/AN76710.pdf))
- **A tall tree shelters you from lightning.** False. It is the second most dangerous place, after open ground. ([NOAA](https://www.noaa.gov/stories/5-striking-facts-versus-myths-about-lightning-you-should-know))
- **You must not touch someone struck by lightning.** False. The body stores no charge. Call 112 and help. ([NOAA](https://www.noaa.gov/stories/5-striking-facts-versus-myths-about-lightning-you-should-know))
- **If you hear thunder, lightning can strike you even under a blue sky.** True. Audible thunder means you are close enough. ([NOAA](https://www.noaa.gov/stories/5-striking-facts-versus-myths-about-lightning-you-should-know))
- **Most of Romania's lightning falls in winter.** False. Winter brings 0.027%. Almost nothing. ([Cristian et al. 2024](https://rrp.nipne.ro/2024/AN76710.pdf))

## What the sources cannot say

Five things this page does not know, though it would like to.

1. No map on this page gives county values, because no published study publishes county values. The zones are indicative, after the three published bands.
2. The page gives no maximum distance at which thunder can be heard. No source read gives a number, and the sound depends on the stroke, the land and the noise around you.
3. The 50,000 degrees are the American service's value for the air around a stroke, not the measurement of one particular flash. Strokes differ.
4. The 25 strikes a year belong to a tall, lonely, instrumented building. The proof is that repeat strikes happen. How often an ordinary roof is hit is a different question.
5. The 760,000 flashes a year mix the flashes that reach the ground with the ones between clouds. The 440,000 count only the first kind. Both depend on how well each network catches what falls.

## How we know

The divide rule and the shelter rules come from the official guides: the Americans of NOAA and the National Weather Service, Romania's IGSU. The numbers about Romania come from two national climatologies, 2010 and 2024, plus the 2018 fatalities study.

The speeds of sound, the speed of light and the temperature of the Sun come from specialist references. The maps use open outlines and GeoNames places. A legend to read once: CG means a flash that reaches the ground, IC one that stays between clouds.

- NOAA / National Weather Service, Jetstream — Lightning Safety https://www.noaa.gov/jetstream/lightning/lightning-safety — the divide-by-3 and divide-by-5 rule, the 30-minute rule, safe shelter
- National Weather Service — How Hot Is Lightning? https://www.weather.gov/safety/lightning-temperature — 50,000 degrees Fahrenheit, five times the surface of the Sun
- NOAA — 5 striking facts versus myths about lightning you should know (2020) https://www.noaa.gov/stories/5-striking-facts-versus-myths-about-lightning-you-should-know — the five myths, the Empire State Building
- IGSU — Furtuna: reguli de protecție https://www.igsu.ro/ — the rules quoted on this page, rendered into English
- Cristian, Zuzeac, Ciocan, Iorga, Antonescu 2024 — A thunderstorm climatology of Romania (1941–2022), Romanian Reports in Physics 76: 710 https://rrp.nipne.ro/2024/AN76710.pdf — 760,000 flashes a year, the zones, the season, the peak hour
- Antonescu, Burcea 2010 — A cloud-to-ground lightning climatology for Romania, Monthly Weather Review 138: 579–591 https://doi.org/10.1175/2009MWR2975.1 — the first RNLDN climatology: over 1.75 million flashes
- Antonescu, Carbunaru 2018 — Lightning-related fatalities in Romania from 1999 to 2015, Weather, Climate, and Society 10(2) https://doi.org/10.1175/WCAS-D-17-0091.1 — 724 deaths between 1999 and 2015; yearly average from 65 to 23.2
- R. Nave, HyperPhysics — Speed of Sound in Air (Georgia State University) https://hyperphysics.gsu.edu/hbase/Sound/souspe.html — 331.5 metres a second at 0 °C, 344 at 20 °C
- NIST — CODATA 2022: speed of light in vacuum https://physics.nist.gov/cgi-bin/cuu/Value?c — 299,792,458 metres a second, exact
- NASA Science — Sun facts https://science.nasa.gov/sun/facts/ — the surface of the Sun: about 5,500 degrees Celsius
- GeoNames — cities1000 (CC BY 4.0) https://www.geonames.org/ — 4,292 Romanian places with over 1,000 inhabitants
- geoBoundaries — ROU ADM0/ADM1 outlines (CC BY 4.0, World Bank / ANCPI) https://www.geoboundaries.org/ — the country and county outlines on the maps
- Storm photograph: NOAA National Weather Service (public domain), via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Lightning_in_Dallas_2015.jpg — lightning near Snyder, Texas, June 2014
- Eiffel Tower photograph: Gabriel Loppé, 1902 (public domain), via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Lightning_striking_the_Eiffel_Tower_-_NOAA.jpg — lightning over the Eiffel Tower, 3 June 1902