Find the speed of sound in air at any temperature, in water, steel and 14 other materials, then turn a lightning-to-thunder delay into miles or a distance into seconds.
How far away is lightning if thunder is 6 seconds?
Find the speed of sound in air at any temperature, in water, steel and 14 other materials, then turn a lightning-to-thunder delay into miles or a distance into seconds.
The calculator below is set to a delay of 6 seconds between the lightning flash and the first sound of thunder, in distance mode, for dry air at 68 °F (20 °C). At that temperature sound covers a mile in 4.69 seconds, so the result gives the distance to the strike in feet and miles and in meters and kilometers.
The usual shortcut is to count the seconds from the start of the flash to the start of the thunder and divide by 5 for miles or by 3 for kilometers. The table in the result shows how far each rule lands from the calculated distance for 6 seconds. Sound travels faster in warm air and slower in cold air, so change the temperature to match the evening you are timing.
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How fast sound moves through air, water, steel and a dozen other materials
At 68 °F sound needs 4.69 s to cover a mile of dry air, and the same mile of steel takes 0.27 s. The calculator has three jobs: the speed of sound in a chosen material, the distance to something you saw before you heard it, and the time a sound needs to reach you from a known distance. Four gases follow the temperature you type; the liquids and solids use measured reference values.
What each box on the form is for
- What to calculate - the speed itself, a distance from a delay you timed, or the time a sound needs to cover a distance.
- Material - four gases, fresh water, seawater, eleven solids, or your own value. Solids are listed for a large block, the way ultrasonic testing measures them.
- Temperature and its unit - only for air, helium, hydrogen and carbon dioxide. In a gas the speed follows the square root of the absolute temperature, so a cold morning and a hot afternoon give different answers.
- Your speed and its unit - only for "Your material", in m/s, ft/s, km/h or mph.
- Delay in seconds - for distance mode: the gap between seeing the flash, the puff of smoke or the hammer strike and hearing it.
- Distance and its unit - for time mode, in feet, miles, meters or kilometers.
- Read the result - the answer in both unit systems, the speed in mph and km/h, seconds per mile and per kilometer, and a note on where the reference value comes from.
Type a temperature in °F or a distance in feet or miles and the result leads with feet, miles and ft/s; metric input brings metric units to the front. Both are always shown.
Nine sounds timed with the calculator
Every result below came out of the calculator itself, with the inputs listed so you can repeat them.
Example 1: a thunderstorm on a warm evening
Situation: Distance from a delay, dry air at 77 °F, delay 6 s
Result: 6,814 ft, or 1.29 mi, at 1,135.59 ft/s.
Dividing 6 by 5 gives 1.20 mi, which is 7.0% short.
Example 2: fireworks a mile away
Situation: Time for a distance, dry air at 50 °F, 1 mi
Result: the bang arrives 4.77 s after the burst, at 1,106.66 ft/s.
On a 68 °F night the same mile takes 4.69 s, so the season moves the delay by less than a tenth of a second.
Example 3: the crack of the bat from the outfield seats
Situation: Time for a distance, dry air at 86 °F, 400 ft
Result: 0.35 s. You see the swing, then hear it a third of a second later.
Example 4: a balloon full of helium
Situation: Speed of sound, helium at 68 °F
Result: 3,307.06 ft/s (1,007.99 m/s), 2.94 times the speed in air at the same temperature.
Hydrogen at 68 °F is faster still, 1,304.52 m/s. Carbon dioxide goes the other way at 267.28 m/s.
Example 5: an ear on the rail
Situation: Time for a distance, steel, 1 mi
Result: 0.27 s through the steel, against 4.69 s through air at 68 °F.
A real rail carries a slower wave than a large block does, so treat 0.27 s as the lower bound. Please do not test this on a track in use.
Example 6: a diver and a boat engine
Situation: Time for a distance, seawater, 1 mi
Result: 1.07 s at 4,921.26 ft/s.
Through air at 68 °F the same mile takes 4.69 s, so sound in the water is 4.37 times faster.
Example 7: a January morning
Situation: Speed of sound, dry air at -4 °F
Result: 1,046.39 ft/s, so a mile takes 5.05 s.
Here the "5 seconds a mile" habit is almost exact.
Example 8: Mach 1 at airliner cruising height
Situation: Speed of sound, dry air at -57 °C, the temperature near 11 km
Result: 294.71 m/s, 1,061.0 km/h or 659.3 mph.
Close to the 295 m/s usually quoted for that height. At sea level on a 68 °F day Mach 1 is 767.7 mph.
Example 9: checking a round number from a worksheet
Situation: Your material, 1,125 ft/s
Result: 342.90 m/s, 767.0 mph, 4.69 s per mile.
That lines up with dry air at roughly 68 °F, which is 1,126.03 ft/s in this calculator.
Speed of sound in dry air from -40 °F to 104 °F
Temperature is the only weather variable that matters much. The table uses v = 331.3 × √(T / 273.15 K), the same formula as the calculator, with T in kelvin. The last two columns are what you would use to turn a counted delay into a distance by hand.
| Air temperature | m/s | ft/s | Seconds per mile | Seconds per km |
|---|---|---|---|---|
| -40 °F (-40 °C) | 306.08 | 1,004.21 | 5.26 | 3.27 |
| -4 °F (-20 °C) | 318.94 | 1,046.39 | 5.05 | 3.14 |
| 32 °F (0 °C) | 331.30 | 1,086.94 | 4.86 | 3.02 |
| 50 °F (10 °C) | 337.31 | 1,106.66 | 4.77 | 2.96 |
| 68 °F (20 °C) | 343.21 | 1,126.03 | 4.69 | 2.91 |
| 86 °F (30 °C) | 349.02 | 1,145.08 | 4.61 | 2.87 |
| 104 °F (40 °C) | 354.73 | 1,163.81 | 4.54 | 2.82 |
Seventeen materials, from the fastest to the slowest
Solids come from Engineering ToolBox measurements of longitudinal waves in bulk samples, water and air from the Wikipedia article on the speed of sound. Gases are shown at 68 °F; in the calculator they follow whatever temperature you enter.
| Material | m/s | ft/s | Seconds per mile |
|---|---|---|---|
| Aluminum, rolled | 6,420 | 21,062.99 | 0.25 |
| Granite | 5,950 | 19,521.00 | 0.27 |
| Steel, 1% carbon | 5,940 | 19,488.19 | 0.27 |
| Stainless steel | 5,790 | 18,996.06 | 0.28 |
| Glass, Pyrex | 5,640 | 18,503.94 | 0.29 |
| Copper, annealed | 4,760 | 15,616.80 | 0.34 |
| Brass, 70% copper and 30% zinc | 4,700 | 15,419.95 | 0.34 |
| Hardwood, along the grain | 3,960 | 12,992.13 | 0.41 |
| Concrete | 3,700 | 12,139.11 | 0.43 |
| Lead, annealed | 2,160 | 7,086.61 | 0.75 |
| Neoprene rubber | 1,600 | 5,249.34 | 1.01 |
| Seawater, typical | 1,500 | 4,921.26 | 1.07 |
| Fresh water, 68 °F | 1,481 | 4,858.92 | 1.09 |
| Hydrogen, 68 °F | 1,304.52 | 4,279.91 | 1.23 |
| Helium, 68 °F | 1,007.99 | 3,307.06 | 1.60 |
| Dry air, 68 °F | 343.21 | 1,126.03 | 4.69 |
| Carbon dioxide, 68 °F | 267.28 | 876.90 | 6.02 |
Lead sits far below steel even though it is denser, and rubber below lead. Speed depends on how stiff a material is against how much mass has to move, and a dense but soft metal loses on both counts.
Thunder, helium and altitude: short answers
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Calculator verified by the LiczGrupa.pl team
Content, formulas and results have been reviewed for accuracy and relevance by our team of specialists.
Reviewed by: Natalia Skrzek