# Lightning Distance Calculator

URL: https://speedycalculator.com/calculators/physics/lightning-distance/
Last updated: 2026-10-25

> The lightning distance calculator estimates how far away a lightning strike was from the seconds between the flash and the thunder, using the speed of sound.

## Inputs

- Seconds between flash and thunder
- Air temperature (°C, °F, K)

## Results

- Speed of sound
- Distance to strike

## Formula

```
Distance = seconds × speed of sound (≈ 343 m/s)
```

## Explanation

Light arrives almost instantly, while thunder travels at the speed of sound, so the delay reveals the distance.

### How to use the Lightning Distance Calculator

- **Seconds between flash and thunder**
- **Air temperature**
- Want to work backwards? Type a value into **Distance to strike** and **Seconds between flash and thunder** is calculated for you.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Multiply the delay by the speed of sound at the current air temperature.

### Inputs explained

FieldWhat to enterSeconds between flash and thunderA numberAir temperatureUnits: °C, °F, K

### What each result means

- **Speed of sound** = 331.3×sqrt(1 + [Air temperature]÷273.15)
- **Distance to strike** = [Seconds between flash and thunder] × [Speed of sound]

### Example values

How the main result changes when **Seconds between flash and thunder** changes and everything else stays at the example values above:

Seconds between flash and thunderDistance to strike (km)31.034.51.5462.067.52.5793.09124.12

## Worked example

Inputs — Seconds between flash and thunder: 6; Air temperature: 20 °C.

Results — Speed of sound = 343.2 m/s; **Distance to strike = 2.06 km**.

## FAQ

**What is the 30-30 rule?**
If thunder follows lightning within 30 seconds, go indoors and wait 30 minutes after the last thunder.

**Is the 3-second rule accurate?**
Each 3 seconds is about 1 km; 5 seconds is about 1 mile.

**What formula does the Lightning Distance Calculator use?**
Distance = seconds × speed of sound (≈ 343 m/s).

**Can I work backwards from the result?**
Yes. Type the result you want into Distance to strike and the calculator finds the matching seconds between flash and thunder.


## Sources

- [U.S. National Weather Service – Lightning safety](https://www.weather.gov/safety/lightning)