What is the speed of sound in air at 20°C (68°F)?

In dry air at 20°C (68°F / 293.15 K), sound travels at approximately 343.21 meters per second (1,235.6 km/h, 767.8 mph, or 1,126.0 ft/s).

How does temperature affect the speed of sound in air?

Sound speed increases with temperature because air molecules have higher average kinetic energy and transfer acoustic longitudinal compression impulses more rapidly. The NASA Glenn formula is v = 331.3 · √(1 + T / 273.15).

Why does air pressure not affect the speed of sound?

In an ideal gas, acoustic velocity depends on the ratio of pressure to density (v = √(γP/ρ)). When atmospheric pressure increases, air density increases proportionally at constant temperature, keeping the speed of sound constant regardless of altitude changes until temperature varies.

Acoustics & Thermodynamics Labv = 331.3 · √(1 + t/273.15) [m/s] • λ = v / f

Speed of Sound in Air & Acoustic Wavelength Calculator

Calculate the physical velocity of sound in dry air across temperatures using NASA Glenn equations, and determine acoustic standing wavelengths.

NASA Glenn Thermodynamic Acoustic Velocity

343.21 m/s(1235.6 km/h • 767.7 mph)

T = 20°C (68.0°F)

Acoustic Wavelength (λ)

78.00 cm

Quarter-Wave (λ/4)

19.50 cm

Wave Period (T)

2.273 ms

Speed in ft/s

1126.0 ft/s

Air Temperature

°C

Target Frequency

The Thermodynamics of Acoustic Velocity

Sound is a mechanical longitudinal compression wave propagating through physical collisions between gas molecules. Unlike electromagnetic radiation, sound requires a material medium and its velocity is governed by the thermodynamic temperature, adiabatic index, and molar mass of the gas.

NASA Glenn Formula (Dry Air)

[m/s]

Temperature-dependent acoustic velocity in standard atmospheric dry air:

v(t) = 331.3 · √1 + t / 273.15[m/s]

• v = acoustic velocity (speed of sound) in meters per second [m/s]
• t = air temperature in degrees Celsius [°C]
• 331.3 m/s = speed of sound in dry air at 0°C (273.15 K)

Laplace Adiabatic Velocity

[m/s]

Derived from the ideal gas law with adiabatic compression index γ:

v = √γ · R · T / M[m/s]

• M = molar mass of air (M ≈ 0.028964 kg/mol = 28.964 g/mol)
• γ = adiabatic index (γ = 1.40 for diatomic gases N₂ and O₂)
• R = universal molar gas constant (8.31446 J/(mol·K))
• T = absolute thermodynamic temperature in Kelvin [K] (T = t + 273.15)

Acoustic Velocity Units & Conversion Equivalents

m/s (SI Base): meters per second

km/h: 1 m/s = 3.600 km/h

mph: 1 m/s = 2.237 mph

ft/s: 1 m/s = 3.281 ft/s

Traian AnghelAuthor & Reviewer

Physics Teacher & Educational Technologist • Brăila, Romania

Last Reviewed: August 2026

Wave Lab calculators are constructed using rigorous peer-reviewed physics formulas from verified metrological repositories. Every equation, spectral conversion, and acoustic property is tested against NIST, CIE, and ISO datasets.

Verified Sources:NIST CODATACIE 1931 2° ObserverNASA Glenn Research

Related Physics Calculators

BPM to Milliseconds Delay

Convert musical tempo into studio delay & reverb times.

Audio Timing

A4 Concert Pitch (440 Hz)

Explore ISO 16:1975 440 Hz standard tuning pitch.

440.0 Hz

Middle C (261.63 Hz)

Middle C frequency, wavelength, and acoustic physics.

261.63 Hz

Universal Wave Calculator

Calculate wave speed, frequency, and wavelength in any medium.

v = f · λ