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Speed of sound

The standard textbook value for the speed of sound in air at 20°C is 343 m/s. A formula line prints 343.2 m/s and a temperature table prints 343.3 m/s for the same conditions.

Also known as speed of sound in air, 343 m/s
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Velocity

Published as 343 m/sPublished as 343 m/sPublished as 343 m/sPublished as 343 m/s

Speed of sound in air at 20°C. OpenStax's ideal-gas result is 343 m/s. Wikipedia's standard-atmosphere formula prints 343.2 m/s and its table prints 343.21 m/s. Engineering Toolbox's temperature table prints 343.3 m/s. The ranked figure is 343 m/s. The 0°C value near 331 m/s is a different temperature.

VerifiedOpenStax University Physics (opens source in a new tab)

In context

  • London to New York in 4 h 31 minConstant · London to New York, 5,570 km great-circle
  • 12× a cheetah's timed top speedSourced · Cheetah, 29 m/s. Sharp 1997, mean of three timed runs over 201.2 m
  • 3.8 football fields a secondConstant · American football field, 100 yd (91.44 m)

Worked out from the sourced figure above, which stays the ranked number.

Mechanism

Why it's so fast

Speed of sound is a reference, not a race. Light in vacuum is fixed by the definition of the metre. Sound is a pressure wave whose speed depends on the medium and the temperature.

  1. Read the conditions

    An exact constant and a speed in air at a stated temperature are both real, and they are not rivals. The entry says which one it is.

  2. No extra figure

    Speed of sound's ranked value is the one the citations print. A coarser rounding is not stored as a second measurement.

Nearby on this list: Speed of light.

Provenance

Every measurement

Claimed, measured and official figures side by side, each with its source. The ranked figure is marked.

  1. 1,235km/h767mph343m/s667knMach1.01Ranked figure

    Speed of sound in air at 20°C. OpenStax's ideal-gas result is 343 m/s. Wikipedia's standard-atmosphere formula prints 343.2 m/s and its table prints 343.21 m/s. Engineering Toolbox's temperature table prints 343.3 m/s. The ranked figure is 343 m/s. The 0°C value near 331 m/s is a different temperature.

    Wikipedia's lead says about 343 m/s at 20°C. The extra tenth of a metre per second is a tighter print of that standard value, not a second measurement. Humidity raises the speed; this row is the dry ideal-gas case the textbook solves.

    Verified
    OpenStax University Physics (opens source in a new tab)

Reference

Specs

Medium
Air
Temperature
20°C
Value
343 m/s
Scope
Ideal-gas textbook value

Context

Background

OpenStax University Physics says that at 0°C the speed of sound is 331 m/s, whereas at 20.0°C it is 343 m/s, and that the ideal-gas formula gives 343 m/s when the temperature is 20°C. Wikipedia's lead says that at 20°C the speed of sound in air is about 343 m/s. The same article's standard-atmosphere section gives 343.2 m/s at 20°C, and its temperature table prints 343.21 m/s. Engineering Toolbox's table of the speed of sound in air at standard atmospheric pressure prints 343.3 m/s at 20°C.

Those are one standard value written to more places. The ranked figure is 343 m/s, the integer the textbook and the encyclopedia lead with. The scope is air at 20°C on the ideal-gas calculation, which has no humidity term. Wikipedia says humidity raises the speed by about 1.5 m/s between dry air and saturation at standard pressure and temperature, so a humid day is not this row. The 331 m/s figure is the 0°C value and is not stored.

Spot a wrong number?

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