Speed of sound calculator
The speed of sound in an ideal gas depends on temperature alone, not on pressure — the density and stiffness effects cancel.
g/mol
Speed of sound
343.2350m/s
- Speed of sound
- 1235.646 km/h
- Mach number of the given speed
- 0.999 32
- Time for sound to travel a kilometre
- 2.9135 s
Show the working
- Air temperature = 20
- Speed for a Mach number = 343
- Ratio of specific heats = 1.4
- Molar mass of the gas = 28.9647
- tk = 20 + 273.15 = 293.15
- Speed of sound = sqrt(1.4 * Rgas * 293.15 / (28.9647/1000)) = 343.235
- Speed of sound = 343.235 * 3.6 = 1235.65
- Mach number of the given speed = 343.235 > 0 ? 343 / 343.235 : 0 = 0.999 315
- Time for sound to travel a kilometre = 343.235 > 0 ? 1000/343.235 : 0 = 2.913 46
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- c = sqrt(gamma R T / M), with T in kelvin and M in kg/mol
At 20 degrees Celsius in dry air this gives 343.2 m/s. Humidity raises it very slightly; pressure does not change it at all.
The five-seconds-per-mile rule for thunder is this figure rounded.